Yeah. Yanking a piece of Cat5 through a tight duct would probably exceed the bend radius and snag it on everything. Still, its easy and cheap to put in now and you may want it in the future.

You can run video over Cat5 if you have the necessary adapters as well. Composite/S-Video + audio or RGB with no audio. I've got one of them actually on my Sky Digibox because it kept giving me ground loops problems.

The budget method would be to use something like a Loftbox but you're basically converting everything to composite so it will look bad.