Just thought I would mention that I had my first ever flawless Orion upgrade !
Went from 9.0 sp2 to 9.1 - after spending 3 hours backing up the servers (learned this from previous upgrades) - but the entire process went without a hitch. (I'm certain that had I not created the - now useless - backups everything would have been a mess :)
I found one minor bug - the .gif icon for 3211.gif is missing in \Inetpub\SolarWinds\NetPerfMon\images\Vendors it was there in 9.0
Also - customizations to CustomPollers-NetPerfMon.Charts are lost in the upgrade.
Unfortunately the upgrade did not resolve Case #35581 for us - that makes it no less than 4 mayor relases (8 - 8.5 - 9 - 9.1) and a number of servicepacks without a solution..
It is however the first time since implementing Orion that we've been down to 1 open Case - so thumps up Solarwinds ! :)