i think the cable i used has a max length of 100m like slaide said, but the ethernet standard for coax is about 500m i think - whatever it is, it's HUGE! and evidence, no i don't have any data problems with my LAN - you've played here before
(ok, 10mbps is slow, but it works!)
when the next gen of wireless comes out (the gen with proper security) i may consider using it to ensure my LAN isn't slowing my cable connection at all.... just depends on money
.... then again..... fibre to the home..... mmmmmmm.....