Instability

[KidGixxer]

Usually ""hacked" roms" have oem's built into the rom. Who's rom are you running? or if you made the rom yourself tell us which kitchen you used. And/or what other oems you might have added to the kitchen.
also you could try looking in the thread the rom makes posted the rom in for similar problems.

[tiermann]

If you're not using a task manager, it could be that you just have a lot of un-exited apps running in the background. The "X" button by default only hides an application in windows mobile.

If hard-reseting is your only fix I don't think that's the problem though as a regular soft-reset should fix that. Sounds more like you have very low storage space, maybe due to a large inbox, temp files, PIE cache, ringtones, pictures, anything like that.

[Maxx134]

list the progs running...
list the rom using...
list what you have done exactly (backups, cleanups)

EDIT:
not all backups & cleanups are safe.,, example:
Member Bushrod in WM6 bug thread :
"If you use Memmaid 2.0, do NOT try Jump To>Tweaks>System Tweaks and click Apply. I did that and lost my SD card. After further testing, even going there and hitting "Apply" without changing anything made me lose my SD card. I could only get it back with a hard reset."

Sory but untill all your steps are realized this is a guessing game .

[datacron]

I am currently running WM6 with the HTC Home and TodayAgenda plugins with complete stability and performance so far.