Depending on your requirements for the migration, you may be able to do the migration yourself.
When we migrated from 6.3.2 to 7.x, we were going from the MSP to the VMware. We simply left our old system intact and migrated the cameras to the new system. We wrote a SQL query to get the data about our cameras out of the MySQL database and import it again using an Excel spreadsheet. Since the old system was intact, we still had our old archives and left the MSP system there until our archives expired over the course of the month. During the migration, since we had our old system intact, we could easily revert back to the old system if issues occurred, but since we tested thoroughly, everything went smoothly. You'll need to work with your Cisco rep to get the appropriate licensing since there are some changes between 6.x and 7.x.
So how difficult this is will depend on what you are migrating to and your expectations for what needs to happen with the existing data.
FYI, we have 7.5 installed in a test environment and haven't experienced any major issues with it so far. However, since this is a .0 release, we are waiting until 7.5.1 becomes available before putting this in production. VSM 7.5 brings a lot of new features to the table, so we want to give it time to mature a little before introducing this into our production environment. So for now, we are running 7.2.1 (although we should probably upgrade to 7.2.2).
