I'd get one....the hardware isn't going to change. It's just a software update that will give us the rentals and other features. No reason to wait in my opinion.
I just bought my 2nd Apple TV and hooked it up today. I love being able to bring all my movies, photos, music, etc. to my tv any time I want. It's going to even better when I can rent movies too. It's easy to use and works very well. I'd recommend one to anybody.