I've had my 990 for 7 months, and in that time done 12000 miles of street and a few multiday hard offroad trips. Here are the mods I have done:
BDCW sidestand relocator
I haven't broken it yet, so I guess that's good. Peace of mind mod.
BDCW second radiator fan[/B]
Stock the bike would not handle slow traffic during Texas summer heat without flashing all the bars at me. Seems to make a difference.
HID Low/HID High beams
Did the high beam after I hit a deer at night. I had no idea how many deer I was driving by before that, and after a few weeks I decided to do the low beam also.
Remus Roxx Ti and 2-1 pipe
Nice growl, louder at low speeds but unnoticeably on the highway. MPG seems about the same, All of the joints on the silencer itself leak exhaust to some degree.
Great for tall guys, I was worried about them rotating but they lasted through a lot of hard front suspension bottoming offroad without budging.
Necessary after I did a mud plow for a few hours that locked up the front wheel a bunch.
Fastway lowboy pegs
Another tall guy mod. Stock pegs are narrowish and hurt my feet after a long day.
Hepco Becker crash bars
Went down tons of times offroad with no issues until the deerstrike at 50mph and resulting slide. They saved my tanks/possibly frame from damage.
[b]Tusk grip heaters
Okay mod, will make a cool day comfortable but definitely not enough to make a cold day warm.
And once the stock scorps wore down I changed to a Mefo Super Explorer rear and a TKC-80 front. The bike has progressively gotten less awesome on the street with these mods, but exponentially more awesome in the dirt. I have not done any SAS removal, cannister removal, ECU programming, throttle camming, or other forum wizard tricks. I doubt I will ever do those things since they cause as much headache as they solve in my experience; I'd feel bad if I ever sold my 450 exc to another person because of how wildly I had to reroute, plug, and modify unlabelled vaccum and fuel lines all over that engine to get to the commonly accepted level of de-smogged.
My only desire now is to get the stock suspension lengthened and sorted for my weight so I don't bottom as hard offroad. The still bike works great as-is.