I have a 950 ADV, which is the carbureted version of the 990. I've put just under 12000 miles on it so far and the only problem I've had is a no-start condition after a tip-over or on hot days. The tanks are vented into a carbon cannister, and if the bike tips over it can cause the canister to fill with fuel...simple solution is to remove the cannister, which is a common mod to these bikes.
The only mods I've done are a new seat (Renazco), crash bars, gps, and one of those handlebar mounted switches to toggle the display.
The 950/990 is a very good street bike, but not as plush as say a GS...it's just more off road oriented than the GS...more suspension travel, lighter, better handling.
FWIW.