Couple this with tools like Jekyll or nanoc (with JavaScript-powered comments, perhaps) and you can easily roll out powerful static sites that are dynamic locally. I can see this getting a lot of use because it makes it so easy to rig up new sites right from the shell. It was already pretty easy but the ability to create a new "site" by merely creating a bucket on S3 reduces the friction even more.
(Perhaps too easy, even.. Rig up a domain registration API, content generator, and an S3 uploader and you could have a script pumping out auto-generated "content" sites all day without any hassles right from your terminal window.)
I think for many personal websites Jekyll[1] style static website generation is going to become very popular. Previously you were always limited by a few dynamic parts of your site such as comments, newsletter registration and questionnaires but now between services like Disqus, MailChimp and Google Docs, you really don't need to pay for any of that anymore. All the dynamic parts of your site are external.
The only cost now is hosting the website at S3 and those costs are substantially lower than competitors. NearlyFreeSpeech[2] is the closest web host to S3 that I can think of and their prices for storage are $10/GB ($0.01 per megabyte month) whilst S3 starts at $0.140 per GB.
If your site gets hit incredibly heavily Amazon S3 will also handle the load transparently. If you find that your site is becoming popular in Europe or Asia than it's also supremely easy to push your site from S3 to CloudFront.
I wonder how far you can take this though? How complex a site can you set up using only static hosting and external dynamic services like Disqus, MailChimp and Docs?
[EDIT] As TeHCrAzY said I ovestated the cost of bandwidth transfer but whilst bandwidth falls rapidly it still falls slower than S3 (at ~10TB of transfer it approaches S3's starting price). More importantly I realised I undestated the cost of storage - it's $10/GB and not $1/GB making it closer to 100 times more expensive than S3.
I also noticed that I'd stated the storage cost as $1/GB whilst it's actually $10/GB (specifically $10.24/GB or $0.01 per megabyte per month) which means that S3 is really far ahead if your site has any substantial amount of content.
The downside to the simplicity of using Disqus for comments is that you lose all your SEO effect from the iframed-in comments - for many blogs the Google-friendlyness of the comments is what drive most of their non-family-and-friends traffic.
How about a service with js commenting that alerts a trusted server of the comment? Server grabs the static html, appends the comment, pushes the new html to s3, bada-bing-bada-boom.
You don't need to even do it with javascript you just need to have a form that submits to your server (like say through a cgi script) which then updates the static file on s3.
Phase 1: Everyone has a static page, without JS, but with animated gifs, counters and guestbook scripts linked from other sites.
Phase 2: PHP becomes popular, static sites are suddenly 'lame', as everyone wants to show off their server-side skills. For some sites, even the CSS and JS, and images are generated dynamically on the fly.
Phase 3: Improvements to JavaScript make it possible to replace server side HTML, image and style generation with the same on the client side.
Phase 4 == 1: You don't need Javascript, simply re-generate the HTML and re-publish it on the site using a script. Sites integrate externals widgets, but somewhat less clunky than before by using JS tricks instead of iFrames.
Hell we've even got sites like Gawker re-implementing frames in JS so they can get all that '90s annoying-ness while still telling themselves they're on the cutting edge.
Previously you were always limited by a few dynamic
parts of your site such as comments, newsletter
registration and questionnaires but now between
services like Disqus, MailChimp and Google Docs,
you really don't need to pay for any of that
anymore. All the dynamic parts of your site are
external.
Is there any good external forum system (google group isn't it due to spam)?
(Perhaps too easy, even.. Rig up a domain registration API, content generator, and an S3 uploader and you could have a script pumping out auto-generated "content" sites all day without any hassles right from your terminal window.)