I know this is a normal stage - every kid gets to the point of wanting to do everything "by self," as Jo puts it. So I'm not surprised - but I do find it amusing, often impressive, and sometimes frustrating.
Amusing because there's so much she enjoys doing By Self that later in life she will hate having to do, from chores to just the regular routines of dressing, brushing, etc. I wish I could feel as excited about brushing my teeth and sweeping the kitchen floor as she does... ("Look Sean! I did it! All by myself!" Comical, no?)
Impressive because she's figured out how to take off her shirts and put her on her socks really well - and I know I certainly wasn't showing her how to do it! She loves puzzles, too, and is getting pretty good at them. The other day she changed several music CDs successfully.
Frustrating, sometimes, because now she tends to strip off shoes and socks in the car, changes her shoes constantly, and demanded we buy her pull-up diapers so she could do that herself, too - a request we were happy to oblige, though so far I've been doing all the pulling up and she's been doing all the taking off and running around naked...
Ultimately, I'm really super proud of her growing independence and I delight in the sense of accomplishment she achieves every time she does something on her own.