I have to admit mine has a nasty habit of getting slow on PR1.2 as well.

On fresh bootup its far faster than older versions, but once its been running a few days of opening/closing applications (or one really heavy day of use) it often bogs right down.

I think its due to moving so much of the OS into eMMC so that when swapping kicks in, it can't keep up with all the eMMC activity. This would seem to make sense as sometimes if I leave it running for a while with nothing open it will speed up again. But you can guarantee as soon as you want to show someone how cool the N900 is it becomes laggy, and I mean "wait a few minutes for it to recover" laggy not just minor stalling.

Sadly I think this is a hardware problem, fitting a full Linux into 256MB is impossible, and by that I mean root size and RAM. If RAM had been 512MB I don't think it would have been half as bad, but we got what was available at the time. As 512MB is standard on new smartphones now I think things will be a lot better, we are just stuck with an OS on hardware which wasn't quite up for the job. Early adopter blues.

Mind you, I have similar problems on desktop Linux if I leave it logged in 24/7 even with 1TB HDD and 8GB RAM particularly with compositing enabled.