It's really not so much tweaks and such as it is just a huge difference in overall performance in Windows 7 itself I think. It's funny how Microsoft seems to be in the pattern of getting every other release right...
Windows 3.1 -- big deal in the day
Windows 95 -- mostly a bomb
Windows 98 -- another hit in its day
Windows Me -- OMG... did that actually happen, or was it just a dream?
Windows XP -- solid workhorse way outlived its intended life expectancy
Windows Vista -- if Windows Me was a dream, that was the nightmare
Windows 7 -- worth the cost of admission and then some. Seriously.
Aside from that... If you haven't done this... you gotta...
http://www.wowinterface.com/download...atencyFix.html
The rest is just a case of not loading your system down with crap you don't need.