Always tinkering with the bikes since I got them. Aligned all the brake pads/shoes, got the saddle angle just right, indexed every gear perfectly (even set the tension on the B screw). Coming from a car background, they're so easy to work on.
Also upgraded my girlfriend's bike as she was complaining about wrist pain. Got her a 29er with head stem extender, bar ends and a wider seat fixed the issue. Now that she actually enjoys riding the bike, she comes on rides way more often.