I'm pleased to see the Folding@Home made the top 10 at number 6. It goes for a team effort by MacRumors members. Most important use is that we are able to assist for gene research of diseases at Stanford.
I already have, and daily use, #2, #3, and #4. Adium is an amazing chat client that I use daily. I just bought the pro version of Weather Pop ($8 ain't bad!). I use OnyX every week to optimize my system.
The only software that I wish was on this list is X-Chat Aqua. http://xchataqua.sourceforge.net/
This is a really cool and free IRC client. I recommend it 100%!
Mreh.... I would never use half of those, and I use alternatives for most of the others. I'd say you'd need SideTrack, CopyPaste, MenuMeters, and some of Unsanity's stuff.