There's only one pair and they're plugged in Roland Green's Trek Fuel, but an all carbon top end is the latest weight saving and ride improving ruse from Rock Shox.
Marzocchi have apparently had problems with their carbon headed RAC fork, but carbon forks and steerers have been going strong on the road for several years. Cannondale's carbon Lefty has also proved highly succesful - if massively expensive - and Pace are planning a completely carbon lower section for their forks. The Black Box (Rock Shox's proto race programme) SID Race's have a totally new one piece carbon fibre composite crown and steerer. This not only hacks out a bunch of weight but also reduces high frequency vibration through the front of the bike in typically carbon fashion.
Trek's star rider, Canadian Roland Green will debut the fork on his home ground World Cup race in Vancouver, and presumably if it stays in one piece we'll see it sneaking onto the top end of the production forks sometime soon.