To bring this up to a round figure:
We stayed at the "glebe country house" in Tarbet, which was located rougly 250m away from Loch Lomond. It had a lovely view on the loch, and Bernadette - the owner/hostess was a really nice person, which made us yummy scottish breakfast (porridge with whisky and raisins), and had a lot of great tipps on what to do/see up her sleeve.
We took a boat tour on Loch Lomond (but sadly missed the opportunity to leave the ship on the other side of the Loch to take a walk there), and made a short trip to Helensburgh to buy some groceries. The Next day we drove the A82 up northwest to Glencoe, and stopped various times just to enoy the very, very beautiful landscape. After taking a walk around an old quarry, and having barbecue on a big pile of roof slate, we decided to get back to the hotel. We originally planned to drive up to Fort William - has to wait for our second visit.
All in all it was a very, very, very nice trip which we both enjoyed a lot!
The only downside, was the driving. The roads in Scotland are in a bad shape, really narrow, and to top that often have small stonewalls besides them. I also had a lot of problems adjusting to Left-hand driving - surprisingly not driving on the "wrong" side, but shifting with the left hand, and the change of perspective (escpecially when parking in reverse).
But this was completly made up by the Scots which always where very friendly, kind and helpfull.