I used FedoraCore before but since I always had trouble with the connection to my Samba server, I decided to migrate to Ubuntu. Right now this Ubuntu running along with my XP-Pro installation. But don't get me wrong, I still hold that MS's OS just because my(office's) machine already had the MS's license for that XP-Pro. Besides, most of my users/clients still hang out with W****** so sometimes I need to login to my XP for troubleshooting, etc.
Btw, Ubuntu is a new GREAT OS in Linux family and it has a chance to beat W******. I love it.