I've been working with EY for two years. I've also had a few SliceHost slices over the years. I've also worked with a dozen other hosts ranging from managed Rackspace servers through Xen and Virtuozzo VPSes down to shared hosts, administered my own Linux server on Internet2 a university, worked for a full service agency that resold white label hosting to over 1000 clients, and I've been building websites since 1994.
The fact that you would compare SliceHost to EngineYard is very very fishy. These two companies are both excellent, but they are not providing services that can even be compared to each other. What I said about EngineYard is not based on "marketing", it's based on considerable experience working with them. I have put them to the test and they have never come up short. I've worked with techs in 10+ countries at all hours to solve problems, and solve them quickly. I think it borders on libel to say they don't have support on hands 24 hours a day, they absolutely do. Rackspace is the only company I've used that matched that level of service and expertise. Try asking SliceHost for help with your server admin, it's just not available. Ezra Zygmuntowicz, one of the founders of EngineYard, literally wrote the book on Rails deployment. They have significantly sponsored Rubinius and Passenger development. The made TextDrive (aka Joyent, originally the "official" rails host) look like amateurs. Their cap recipes gem and stock monit scripts are more comprehensive and reliable than anything else I've seen anywhere else.
As far as the database sharing issue is concerned, the purpose of sharing is to allow you to save money by using only the resources you need. It's not true that all database machines are shared. They have spec'ed them out and refine based on the amount of resources need by on actual usage of their clients. If you get to the point that you actually need a dedicated database server than they will gladly provide that to you. At that point you will probably need multiple dedicated app servers as well, though of course that depends on the particulars of your app. In any case, I can't think of anyone that can build you a better Rails cluster. Sure you pay a premium for their expertise, but that experience is currently second to none.
My comparison of SliceHost to EY is also based on actual experience deploying large scale sites. EY claims to offer all the services in the world, but at the end of the day the technology they delivered was sub par. I understand all of the things you say about Ezra writing the Rails deployment books and their support of the community. None of that changes the fact that their offerings are vastly over priced for what they deliver.
I've been building web solutions since 1994 as well, and have built dozens of web sites for Fortune 50 and better companies. I fully understand what it takes to scale out an architecture to 30,000 transactions per second at 30% average cpu utilization, or to deal with 70 Terabytes of text and images in sub second response times. I've built arbitrarily deeply nested hierarchies with 100's of millions of items that have to return their result sets in sub-second response times. I don't mention this to brag, but to illustrate that I have substantial system engineering and architecture background.
I'm not sure how you can say that comparing SliceHost to EngineYard is "very very fishy". It depends on your perspective I guess. EngineYard seems to cater to companies that don't have strong in-house database talent, or who aren't comfortable with certain things like creating a Capistrano deployment file or basic sysadmin tasks. If you are comfortable with those things though, when you compare what they do with what they claim, they fall very short imo.
The thing with SliceHost is that they focus on one thing, which is delivering virtualized resources. And they deliver them fast. You can have a new slice up and running with SliceHost within minutes, where with EngineYard that same tasks takes weeks. On multiple occasions we had to escalate to one of the company owners before we got a new slice created.
So perhaps for my background, and for the needs of the companies I've been at, maybe EngineYard's services weren't a great fit. I'm willing to give them the benefit of the doubt. If you just need virtualized resources though and are comfortable building out your own architecture from there, EY may not be the best fit.
I do find it interesting that you mention Rackspace's service, considering they bought SliceHost sometime ago.
If you have the manpower and talent to administer your own servers then clearly EY is overpriced. However the cost of acquiring said talent is significantly higher, and much riskier for smaller companies. My experience is not at as big a scale as yours, but I can see how there are increasing economies of scale of self-administration (and purchasing your own hardware, etc) as you get bigger.
However my beef is saying that you had better luck with SliceHost than EY, which to me is a non-sensical comparison. SliceHost doesn't offer any of what you're paying for at EY. However you explanation clarifies things significantly for me. EY is not very good at SliceHost's core competency, I'll tentatively agree with you here since I haven't done a lot of Slice commissioning on EY.
The fact that you would compare SliceHost to EngineYard is very very fishy. These two companies are both excellent, but they are not providing services that can even be compared to each other. What I said about EngineYard is not based on "marketing", it's based on considerable experience working with them. I have put them to the test and they have never come up short. I've worked with techs in 10+ countries at all hours to solve problems, and solve them quickly. I think it borders on libel to say they don't have support on hands 24 hours a day, they absolutely do. Rackspace is the only company I've used that matched that level of service and expertise. Try asking SliceHost for help with your server admin, it's just not available. Ezra Zygmuntowicz, one of the founders of EngineYard, literally wrote the book on Rails deployment. They have significantly sponsored Rubinius and Passenger development. The made TextDrive (aka Joyent, originally the "official" rails host) look like amateurs. Their cap recipes gem and stock monit scripts are more comprehensive and reliable than anything else I've seen anywhere else.
As far as the database sharing issue is concerned, the purpose of sharing is to allow you to save money by using only the resources you need. It's not true that all database machines are shared. They have spec'ed them out and refine based on the amount of resources need by on actual usage of their clients. If you get to the point that you actually need a dedicated database server than they will gladly provide that to you. At that point you will probably need multiple dedicated app servers as well, though of course that depends on the particulars of your app. In any case, I can't think of anyone that can build you a better Rails cluster. Sure you pay a premium for their expertise, but that experience is currently second to none.