Please install HTop on your device. Then you start it when your device is slow and can see what's eating the CPU time.
IMHO, there is still something wrong somewhere in the OS. I'm especially scared of Tracker, the indexing engine, running amok. This has happneed already a few times on my N900s.
(Instead of installing something, you could also just do "top" in x-term, or "tracker-status")
The 2nd thing is that input touches sometimes aren't recognized or then as doubletaps.

I' say this is the price for witnessing the birth of a new, vastly superior mobile computing and communication platform