The new Xbox has a tentative release date of Q4 2013. If you've got the $100 for a used 360, I say go for it. Craigslist is your friend. Should you buy one new? No. Stick to used.
For instance, as much as I love PC Gaming, I love my Xbox 360. I sold my Slim 4gb about 4 months ago and missed it so much that I went on Craigslist and got a MW2 Special Edition 250gb with one controller, COD Black Ops & COD MW3 for $140. Money well spent.