Bob, the 2008 F650GS is a 798cc parallel twin based on the same frame as the 2008 F800GS. I am waiting for my '08 F650GS to arrive at the end of this month or early May.

I ordered it before Xmas. Actually I ordered the twin 800GS but it got held up in production so I was asked if the twin 650GS would be OK. I said yes as I had already sold the single F650GS and I don't want to have to push LRB all summer. Glad I said OK to the cheaper 650GS as once the bottom line is reached with all the add-ons....holy smokes the price goes up!!!!! Over 50% higher easy!

The 800 has a 21 inch front wheel....the 650 has 19 inch front wheel
800 has sturdier front forks and more play.
800 sits much higher......lowest the 800 goes is 33.5 inch seat....650 has a 31.1 seat/or lowered frame for a low, low 29.9 inch.
Handlebars thicker on the 800.
Spoke wheels for the 800; cast alum. for the 650
twin discs on 800; single disc. on 650
85hp on 800;71hp on 650 (done by softer cams and valves not lifting so high, bore and stroke the same.) Gear ratios and torque range different.
800 weighs the same as LRB:456lbs. wet. The 650 will be about 437lbs wet.
Touratech has lots of accessories already. All other aftermarkets trying to catch up quick.
Probably more stuff but I think that for me I got lucky the 800 was delayed and I am getting the bike best suited to my size and needs...OK wants.!!

USA is getting the F650GS this July I have heard. At first they weren't getting it at all this year. 800 coming later this Fall as a 2009 model I hear. Always rumours with these bikes. Production and Marketing evidently in different buildings!
I have been following the forums on the 2 new twins all winter avidly. Europeans already riding theirs!! First blip: stalling out.
I got all the dirt pretty well. Boatload of F650GS destined for BMW Canada have been stuck in the clay in the St. Lawrence River since March 8th. Being onloaded and on their way to Montreal by now I think. My bike was not on that ship but on one passing it last week some time! The ship that was stuck lost its engine during our last big wind snow storm across the upper States and St' Lawrence River valley. Remember last year when a boatload of BMW bikes fell into the sea for salvage off France was it??? Sure would be cheaper that way!!