I like to a do a reinstall of the OS and then use the latest Combo update about once a year. No good reason for it, don't know that I notice any speed difference, just feels like good housekeeping after there have been 5, 6, or 7 dotted updates to the OS.
I did this back in Feb, but half of the impetus was related to repartitioning my HD to give more to Windows. So, I made sure my Time Machine backup was up to date, used Winclone to backup my Windows partition, then booted off my MBP DVD. Repartitioned my HD and reinstalled Snow Leopard from scratch. Then ran the 10.6.6 combo update, then used Time Machine to restore my user data and applications, then used Winclone to restore my Windows computer to the Windows partition.
All has worked great since. No noticeable difference in speed one way or the other. I tend not to have any problems anyway, though, and have never had a kernel panic with this Mac in little less than a year.
(Okay, not entirely true, it did kernel panic when I tried to use the Snow Leopard retail DVD to boot from when I did the rebuild, but that makes sense, 'cus the original SL DVD wouldn't have supported a 2010 MBP).
Cheers.