I had one.
Here's what it was:

If you do take an interest in this bike, make sure to take it for a test ride.
When you do so, take the bike onto a flat road. With the engine fully warmed up and the choke off, ride in first gear at about 3000 - 3500 RPM at a steady speed.
If the bike surges, don't buy it.
The First Year R1100RS is known for various characteristic failures, from transmissions to fuel pumps to speedometer cables. It also had several quirks, including rims that bent fairly easily, and shocks that didn't last very long.
There were also several recalls performed on it.
If the seller has a complete record of services, repairs, and recalls performed on it, that would be good.
All that said, I enjoyed riding it, when it wasn't in the shop.