I'm mid trip on an 800GS, currently in Malaysia after leaving the uk in May last year.
I have to say as a ride goes the bike has eaten up everything thats been put in front of it including some really hard off road in Tajikistan, Kyrgyzstan, Pakistan and Nepal. As a bike goes it can deal with anything off road you want to put it through and is also great on the road as well.

On the flip side, there seem to be a few mechanical issues. I've heard of chains suddenly going but this hasn't happened to me yet. I'm on the original chain and sprocket set and i'm on 23000 miles.
The weakness seems to be the fuel pump. I had mine go on the way from the airport to bangkok and i also meet a group of italians making a film for BMW who had the same issue in Tajikistan. Saying that it's a car fuel pump that should be available in all countries.

The forks seem to be as strong as an ox. I saw a bike in the penang BMW office that had been virtually folded in half after hitting a wall and the front forks weren't affected at all.

btw, i've had 2 crashes, once run off the road and the other hit by a jeep on the wrong side of the road going round a bend in Pakistan. Both times the bike was strong enough to stand up to it.

Whatever bike you get you are going to have problems along the way. New or old the bikes take such a battering that you will always have to fix it on the way. It's all part of the fun.

As far as the comments about keeping the bike going a slow speeds.
Couldn't disagree more, I've been a virtual standstill on tricky tracks and it's always been responsive and complient and i'm no expert. I've only been riding for 2 years and my off road riding had only consisted of a weekend off road course and a couple of weekends on salisbury plain before i left the UK.

Good luck with your choice.

Russ