That's an excellent pick up mate, well done! All BMW's a great bikes (I can't think of a bad one, actually) and the F650's have proven themselves to be excellent for commuting duties, right thru to crossing continents.
Make sure you give it a full service including oil, spark plugs and all filters, (BMW fuel filters need to be changed regularly) I'm guessing that your generous friend wasn't big on maintenance, considering how much he disliked the bike, so that'd be my first priority, to give it a good service.
Replacing fork seals is a simple task, so do that sooner rather than later, or you'll end up with a fork leg full of rusty goo, if you don't already. And park it under cover, I can never understand why people leave their bikes parked in the street, that's just asking for trouble! Cheers, Terry.