The Ethernet leads are a LOT faster than wireless (so I'm told by the gamers that come in all the time), 30m is the longest lead we keep in, £10, so cheaper than eBay
i'm an xbox live gamer and i use ethernet, and i swear by it religiously!
i have 2 slimline 360's, both with wifi but i have my main one connected to ethernet and my secondary bedroom one on wifi and i can notice a difference in connection speeds.
(granted i do have fibre optic broadband which helps matters too)