I think this is probably related to the "Slow and unresponsive after 3 days" thread. (Even though in this case it is happening in less than a day)

I have the same issue, probably at first I didn't notice through my rose colored N900 glasses, but it has become quite a bottleneck.

Unfortunately in my case all text messages arrive with the same sluggishness, so it's perhaps more complex than just a swap issue. I have very little installed these days - almost factory standard, no widgets other than simple calendar.