I have read quite alot of info on bettas since aquiring mine and I've just recently gotten 2 1 gallon plastic tanks (and another betta) and plan on getting another for my 3 new guy here soon.
You are so right, they really are much more active in a larger tank. I've noticed that Mr Limpet is constantly swimming around now. He seems to love his new place Now I just need to find something small to put in it.

Thanks for all the info!