There are many ways to speed up windows mobile and particularly to HTC Touch Cruise (I’m not sure if this is generic to every other mobile devices, but you can give it a try), I found that to disable all the button contributes the biggest speedup. So this is what I do in the Start->Settings->Buttons:
I disable all the buttons and set all the buttons to "None". Once it is done, I found that the speedup is tremendous. The only most useful button in my opinion will be the Button 3 - Camera which you can still enable it for convenient purpose while you're taking photo. Hope this tip helps.
p/s: One of the things that I’m VERY NOT satisfy with PDA is the slowness in the software. Disable all the button seems really speedup for at least HTC Touch Cruise device and I hope it is applicable to your mobile device too.