Having just upgraded yesterday, here is what I've found so far:
1) WebHelpDesk 12.0.1 and its asset syncing is incompatible with JSS 9.21. JAMF significantly changed the table structure in Casper 9 and Solarwinds hasn't yet upgraded their product to be compatible. They claim they're working on it but for now we're playing the waiting game for an update.
2) MySQL 5.6 and higher introduced a new security feature that throws a warning message when you do a mysql dump, so what's happening is that the JSS Database Utility is failing with this error message and the DB is not being successfully backed up every night. I'm still looking for an adequate solution for this and may be contacting JAMF soon for some tech support. Not sure i want to back grade to MySQL 5.5…
3) I saw some squirrelly behavior with clients that tried to run a policy but that had not yet gotten the new 9.21 binaries. The policy would fail claiming that it couldn't communicate with the CasperShare AFP share point, so the policy would fail. But then once they had successfully run their daily inventory update policy (which upgrades the binaries and Self Service to 9.21), the policy would work again…
4) The other big hurdle is that it's just going to take you some time to learn the new interface. It's better in many many ways, but it's different. Some things are in radically different places. Overall, it's a more logical layout and it's good, but give yourself some time. I'm still finding little surprises every time I dig through the interface.
