I have been playing with it doing the tutorials for a little over a week now. I think it's pretty cool, but there's a lot of room for improvement. I'm sure in time Google will improve on it and add to the current functionality. A few limitations it currently has at the moment, is there is no way of publishing to the market or posting the resulting .apk to your or another website for others to try out your app and there's currently no games module or ability to do graphics that I've found. These are just a couple things.
It took somewhere around 2 months before I received my acceptance. I plan on using it as a prototyping or proof of concept tool, for a few app ideas.
Performance wise, I haven't experienced any issues, I'm currently using the Android Emulator for testing instead of my phone, because I'm using it under Linux and couldn't get it to connect to my phone. I haven't tried it under Windows.