We may stick with BESX once all our mailboxes are migrated to Exchange 2010. Personnaly I like it and it seems to fit the size of our organazation. I really only oversee abour 45 blackberry users.
upgraded 10 BES and 10K users from 4.1.6 to 5.0.2 three weekends ago using in place method. Seamless upgrade, no end user complaints. The BAS interface seems to have about 50% of the functionality that the 4.1 console had.