Mixed works fine. The coax is limited to 10M only. Check your UTP cables... Cat 3 is limited to 10M, Cat 5 is good for 10M or 100M. Hanging a UTP hub off of a coax run acts just like any other device hung on that coax run, no problems there. Keep in mind that you have a limit of 100 meters on a UTP segment. I think I remember that coax (thinnet) is limited to 300 meters.

One issue that crops up occasionally with UTP is daisy-chaining the hubs. Try to have no more than 3 hubs between any two points on the network. Timing issues start getting very wierd after that...

A buddy of mine (with more money than sense!) has a two story house. His play-room is upstairs and has a 8-port hub and 7 machines. His wife then wanted a computer downstairs in the living room. She then wanted one in the kitchen, then one outside on the patio... Well he ran one wire to the living room. Then put in a hub and ran a wire to the kitchen, then put a hub there and ran a wire to the patio. Everything was fine until he got a cable-modem... You guessed it. He added another hub between it and his play-room. We had a devil of a time finding the problem because it was very sporadic, it only cropped up occasionally when he had a computer hooked up on the patio! We cured it by putting a larger hub in the play-room and removing the hub between the cable-modem and the play-room.