we upgraded from 9 to 10 not too long ago. It was pretty smooth though that stated we were not using any policies or standards to migrate. That was a step we did not have to worry about
The only item I had a problem with was the upgrade of the ECS whichwasn't a big deal. we have only six QE's so I removed then re-installed the QE's in our production area and testing area to finish the installation
Now the CCS_Web part took some doing. Although it appeared to me in teh documents and was mentioned when I called support...I did not have to have SSL setup for the ccs_website. I DID need to make sure that each the application and certificate server inmy distributed setup were trusted for delegation..not just the account I use with the system.
Other than that it was smooth...minor bumps nothing too serrious. A LOT easier than going from 8 to 9