Guys, shared hosting is designed for the 99% of non busy sites, say under 1,500 unique visitors a day, with the level of traffic HN is doing I'm surprised Pair didn't warn you earlier. A site this busy needs a dedicated server or virtual server.
That is why shared hosting is cheap, you start with it and once you are successful or starting to get slashdotted you buy something bigger that can scale.
Also, just going to point out here that Pair.com has had a great reputation in the hosting industry, and has for the last 10 years.
I've been in the industry for 10 years and worked for quite a number of hosting companies, not Pair though, and when you have 150 shared clients on a machine and 1 client is causing the problems you do your best to deliver the warning before it gets out of hand but it is very hard to do.
When I emailed Pair.com to tell them that my site was about to get a writeup in the Wall Street Journal, they moved my site to a dedicated server within an hour, left it there until the spike of traffic was over, then moved my site back to a shared server--all at no charge. If you use Pair.com properly, they are more than excellent.
I don't think anyone will disagree. What they will assert, however, is that shutting down a site with zero notice is a jerky thing to do. As the other commenters have said, the nicer/smarter thing to do would've been to send an e-mail that says "Hey, you're using too much bandwidth/whatever." The smartest thing of all probably would've been, "You're using too much. Want to by more?"
That is why shared hosting is cheap, you start with it and once you are successful or starting to get slashdotted you buy something bigger that can scale.