I think I'll give myself a mountain bike this christmas.

For years it was pointless to own one in my area--trail access was really limited. I haven't owned one for a looong time, and know nothing about the latest and greatest components.

I thought I'd tap the vast knowledge of PdC contributors to get oriented.

Am I better off building or buying?
What brands currently rule? My LBS stocks Felt.
What are must-have features--disc brakes? full suspension?