We finally jumped from 2007 sp5 to 2009 sp4 about a month ago. I found it to be a real easy transition and we have had very few snags. Everyone picked up on the new UI enhancements pretty quick and most think they are improvements and lead to time savings while modeling parts.
The negative that I have realized is that for the few glitches that we have come across, it is too late to submit them as SPR's since the last SP has already been released for 2009. That's why hopefully in the future we will upgrade a little earlier in the calender year (sp3 or so).
I have installed 2010 on my machine to test, but I have to wait for an admin to install the license manager on the network. Hopefully that can happen soon. There are quite a few enhancements I am anxious to try out.
Solidworks 2009 SP4.1
4GB Ram
Quadro FX3700
2.66GHz Core 2 Quad XP Pro SP2.0