Just to touch on a few points:
1. The 10Gbps specification now being drafted recognizes that CAT6 cable may be supported over limited distances (up to 10-15 meters, for use in datacenters); full 10Gbps support will require an augmented "CAT6A" cable with performance up to 500Mhz rather then the 250Mhz of CAT6. The 30% cost premium of CAT6 over CAT5E is only worthwhile if it actually buys you something :-)
2. It's not just cabling, but all connectors, terminations and installation practices must be CAT6 complaint as well. These can carry even a larger price premium then the cable.
Personally, I think CAT5E is the way to go right now in terms of price/performance on a home structured cabling system.
3. Look into installing a proper structured cabling system for voice, data and cable. Leviton, Siemon, etc all sell "media centers" where you can consolidate all your wiring and cross connections. ie:
For instance, I put a panel in the basement and ran two CAT5E and two RG-6 cables to each wall plate location. This gives you complete flexiblity in terms of connecting two computers, a computer and a phone, etc. The two coax allow one for cable tv, the other for a roof antenna, or a direct connection to a cable modem, wherever. The basic idea is that the cabling in the walls in permanent, and by connecting patch cables at the wall plates and the panel you can connect anything to anything.
The residental cabling standard actually calls for two CAT5E, two RG-6U ::::and:::: two multimode fibers....but i think that's getting a bit silly :-)