While I may be in danger of committing a "Bill Gates" (Who needs more than 640k RAM?), but I say go with Cat-5E.
If you run Cat-6, every piece of the system must be Cat-6. All the punchdowns, all the patch cables, etc. Cat-6 components are twice the price (or more) of Cat-5E. Even with fiber-to-the-house, the top download speed is 30, while you can get 1000 out of a cat-5E install. I just don't see the need in a residential setting for Cat-6.
As for anything involving predicting the future, it's an interesting question. It will be interesting to see what everyone else thinks.
I'm sure of one thing though. Make sure that you (or your installer) do a quality installation. A good quality Cat-5E installation will blow the socks off of a poor quality Cat-6 installation.