I found a very enlightening article about GC in Ruby that I think really applies to every interpreted language: http://viewsourcecode.org/why/hacking/theFullyUpturnedBin.html
Basically the point that ‘the GC will clean up your memory for you so you don’t have to worry’ is really untrue. When you are doing a large amount of work the way your code behaves dictates how the GC will behave. For example, if you decided to contcatenate a bunch of strings you’re going to get burned with memory usage going through the roof. This is unacceptable in a lot of situations, especially on a server.
Also I the writer _why apparently was a big figure in the Ruby community until his mysterious disappearance in 2009. Weird. Read about him here.. I wonder why he quit?