I like it, and to me it was worth upgrading. I used most of the basic hardware tweaks that were listed (PIIIeb tweak for instance) but I really like the easy editing of Outlook's (2000/2002) annoying file attachment lockout where you can't get to certain attachments, and the easy access to certain memory settings (like not paging the kernal). It has some cool stuff that I like, so for me it's worth buying. Try out the demo, and see if you like it first. The demo time period gives you enough time to fiddle with it and see if you like it.

Thank you Clutch, I'll give it a try and advise !

download powertoys for xp and you'll get tweakxp for free...

You're confusing TweakXP with TweakUI (which although also very useful is not the same thing).

Soryy about that...should've known! ;(

I downloaded the evaluation version of TweakXP.Assides the several tweaks that are useless for me, most of the things you can do yourself from the registry.
Take a look at
http://www.xp-erience.org/sections.php?op=viewarticle&artid=14