1-2 hours is way too long to deal with a Digg/Slashdot spike. Heck, our servers take 1-3 minutes for the cache to catch up and even that is too long to handle a traffic deluge.

We can take 1500 simultaneous users and we've spiked to 9000 users when serving from cache. With 256 MB of RAM, you are dead in the water after a few hundred people (especially on a mysql-based forum).

If it takes you 1 hour to recover from a spike, you will have lost thousands to tens of thousands of readers. You don't want to overbuild for this site, but you also don't want to cheap out and underbuild.