Well I just jumped through the hoops again installing a new tool, and as it took me quite a while, I thought I'd help the Internet at Large through it. Or at least make a few notes, as most of my own searches for information on this drew blanks. I even went to the lengths of translating a few obscure German posts in case they could help.
Anyway, munin, once you get it going, is actually quite cool. It provides you with a graphical look at your server performance, and you can customise which data you collect quite simply. I'm installing it on an Ubuntu server 11.04, with nginx and mysql. I'm expecting a big traffic spike in the near future, so I want to see how the machine is handling it, and which bits, if any, are struggling.