I've got an e60 myself. 4.4L v8, the car gets up and goes. No problems with it, and I've got 82k miles on it. A few electrical quirks here and there, but it was all fixed via DIY and trial and error. They're very picky cars when it comes to electrical. It should be expected, with all the sensors and what not.
If you're going to buy one, I'd say get one with a warranty, unless you're a very DIY-savvy person. Repairs are not cheap. Oil for my car is 8qts, costs about $80 just for oil and filter, to do it myself. The potenzas I've got on it are about $280 a tire. I did get in an accident and the headlight assembly alone was $1700. I wasn't at fault, so I didn't have to pay it. Total came to over $5k, new headlight, bumper, and quarter panel was all it was. Parts alone are expensive, labor is just downright sad if you take it to the dealer. Indy shop is the way to go.
My apologies for the odd photo effect, I was experimenting with some different HDR stuff with exposures.