I originally installed a beta of 7.0, then upgraded (and upgraded, and upgraded...).
Everything worked OK, except that the update to SME 7.3 introduced a problem that only existed because I had started with a 'beta' version.
The official line at the time of the 7.0 release was that upgrades from beta to release versions are not supported; I would assume that the same will apply this time around.
Note that I could have avoided the problem I ran into (I'm sorry that I don't remember exactly what it was) if I had backed up my beta system, installed the release version, then restored the backup.