I've just un-jailbroken.
I found it made my screen unresponsive and laggy, and even the quickest press sent my icons jiggling to re-organise them. Very annoying. I also found apps crashed more often.
The only apps I was interested in from cydia were:
Winterboard - I can live without this, though I liked having wallpaper and hidden names
FiveIconDock - that was handy to put phone, sms, ipod, mail and safari on the dock. But I can live without it.
Backgrounder - never used it, don't really need it
SBSettings - vaguely useful, but didn't use it day to day
IntelliScreen - I liked this and wished my phone did it anyway, but it wasn't worth the problems I had.
Each to their own. Personally, I found only IntelliScreen was worth jailbreaking for.