Were you planning on putting any material to those rollers so you can get more forward/backwards traction with the carpet? In my oppionion omni's are great if you can make a nice balance between traction on the carpet and still being able to slide sideways. We had thought of omni wheels before on my old team but couldn't find a simple enough way for us to power them well and gain some traction with them. We had pretty much what you posted as they are and then we decided it was just wasn't worth the added weight with little traction gain so we put teflon skids instead. (263, 2001-2003's robots)
They are none the less very nicely done. I would suggest going with some added traction device on the rollers if possible, but either way you do achieve the nice turning bonus of the omni wheel design.
In an effort not to sound stale but unable to think of a way not to... You could look at the technokats omni, or trickwheel whitepaper.
http://www.chiefdelphi.com/forums/pa...le&paperid=226
Its a very good example of one way to add traction to the omni wheels while still being able to turn great. Personally I have driven the ball drive robot these were on last year and they worked very nicely.