After having my myTouch for a few weeks, here's stuff I'd like (in no particular order):
1. faster hardware -
Would be nice
2. multitouch (make screen more responsive) -
Multitouch is available for rooted users and the newest Donut kernel supports it.
3. some sort of task manager that lets me force stop/kill background apps -
On the Market, almost definitely need root
4. a standard widget theme (for uniformity, but I doubt it'll happen)
5. a faster browser and flash, dammit...flash support -
Flash is on Hero builds, need root. You can try one of the alternative browsers on XDA, or flash a newer ROM based on Donut code, browsers on the XDA roms are pretty fast from my experience.
6. scientific (or even graphing) calculator integrated into calculator app -
On the Market
7. more widgets (so many apps don't have one when they should) -
There's a lot of widgets, what are you looking for specifically?
8. make the built-in smilies 2-characters instead of 3-characters
-for a mobile OS, this seems to be a huge oversight.

is no better of a smiley as

. the hyphen is a waste of texting data. fine by me since i have unlimited texts, but it seems like a really stupid decision. none of them need 3 characters. -
I would prefer 2 as well.
I'm forgetting some stuff, but those are my main concerns. I'm loving the phone and Android, and my next phone should be that Xperia (if it doesn't cost a fortune). PEACE.