The thumb strap works brilliantly.
Super Mario 64 DS got slammed because of the lack of analog controls keeping it from being the “killer app” for the DS but if you switch it into touch mode and either use the stylus or better yet the thumbs strap, it becomes a killer app because of the beautiful controls it creates.
The stylus is not nearly as good as the thumb strap when it comes to controlling this system and once third party (or possibly Nintendo) companies create new stylus thumb devices, it will become even that much better.
I am just waiting for companies to take advantage of the ability to hook up to the WiFi Internet connection so I can PictoChat with people around the world or play Madden against someone far from me.
The batteries lasted 2 full days of me playing plenty each day before the battery light went on. Assume 4 hours each day before the batteries showed signs of slowing down but I had volume all the way up, turned the system on and off plenty of times, and never once shut off the back light.
I can use all my carrying cases for the original GameBoy Advance (not SP) so that saves me money there. The power adapter is identical so I already have a bunch with my older GBA systems (yes, systems, I have 3 GBAs).
This is a semi review, I’ll keep posting to this thread with more impressions of the unit.