We completed our upgrade last week.
I ran into two issues. The first is likely unique to us.
1) The install completed but we ran into problems during the configuration. A critical error occured. We had to reconfigure each solution and then where missing tables and stored procedures. After working through each of the config files, we were able to piece together the SQL that didnt run to address those issues.
2) There is a bug in 7.6 that was fixed in later releases of 7.6 but did not get addressed in 8.0. The Update Network Location Resource task will remove the location association to your device if the location does not have a matching subnet assigned. We had 15,000 devices without a location. Luckily we had another system that had the same information and we were able to restore from that. So if you assign locations, make sure to disable that task until you get a fix from Symantec.
Everything else has gone great for us. Less than 50 actively communicating agents to upgrade. It is usually a few weeks before I get to that level. The new agent provides a wealth of information that we previously didnt have when checking agent health. Over all performance seems to be a little better.
Follow the Symantec checklists for upgrades, make sure you have good backups. Throttle back all agent communication. We default to a 2 hour agent checkin period, we bumped it up to 12 hours before the upgrade.
Disable inventory for a couple of days.
Slow upgrade your agents, I can send you the filters we created to only allow X number of clients to update at once. As more get updated and you dont see any issues you can slowly start to increase the numbers as well as slowly decrease your agent check in.
I gotta say, even given the issues we had, this was by far the smoothest upgrade we have had yet.