Several years ago, when the SlashCode 0.2 code came out, a friend and I basically rewrote it in C, with Postgres (6.5 at the time) over a weekend and ran if for about a month. It was my first real experience with MySQL. I haven't looked at the code lately but if that was the base, there were numerous areas where the SQL could be improved. I still think Slashdot threw hardware at a performance problem, but I don't know enough about.
I've been slashdoted and maxed out at about 6 hits/second over about 3 hours to the specific page that was mentioned. The increase on the rest of the was not that substational. We basically ended up creating a geocities site for the images, but the P133 with 128MB of memory and Linux 2.2 handled it well. The only real problem was that the Apache/Jserv (at the time) combo got a little slow getting the pages going (all pages were .jsp's). We ended up having to tune the kernel a bit and do a quick reboot.
I did have an OpenACS 3.2.5 development site running and (unknown to me) it was included in a E! documentary and received 5 hits/sec for 2 hours without a problem while the show was on TV. I did move the site back to the pre-OpenACS code during the replays, but that was mainly because the site wasn't finished.
Hope that helps you a bit.
