I have successfully upgraded to Orion 8.1, with a large db (30G+) and can confirm that several outstanding issues have been resolved:
Nightly DB maintenance runs in 30 minutes, not 4 hours
Advanced Alerts not linking to corresponding interface ID - works (ticket 2149) http://www4.solarwinds.net/SolarWindsForum/topic.asp?TOPIC_ID=3235
I'll be doing additional work with my Advanced Alerts and Custom MIB Pollers, but so far Orion 8.1 has significant performance and functionality benefits!