I've overclocked my TP2 and it made a notable improvement on playing back a video and some other things.
I have a high bit rate video on my flash card(a kids video to keep my little girl happy) playing back with media player will cause it to studder and be choppy (almost unwatchable), after overclocking to 756mhz or 806mhz, the video will play back perfect, no sudder or choppyness.
Other times with some HD games designed for the HD2, I can get a semi-ok running game running pretty good with overclocking.
If you think you'll over clock and your phone will become a HD2 (1ghz CPU about same size screen), it's not going to happen but, if there is a app that just runs a little too slow, it will help. It will even help the OS speed but, very little.
DOn't be greedy with speeds, with the good there is some bad, if you over do it too much, you'll notice more lockups, just lower the speed and test, there is a happy medium.
I posted in the overclocking thread about my settings, it did help...
http://forum.ppcgeeks.com/htc-touch-...-settings.html