So, I've rolled a new character, that being a human priest.  Two guild-mates made priests at the same time.  On is going Shadow, the other Holy.  My questioin is, is Disciple really worth it or should I just go Hybrid between shadow and holy?  Not sure as to what the advantages and disadvantages of a Disciple speced priest is.  Anyone out there speced in Disciple?

well for a start dont go shad/holy spec :S wen ur in shad form u cant cast holy spells... anyway discs are one of the best survival classes at 70 with there excellent buffs they re hard to defeat they are also popular for the arena

A pure Disc build is nice for leveling and excellent for arena, but not really a whole lot of use in PVE.  The buffs they offer deep in the tree just have CDs that are too long to be worth a lot in PVE.  However, the early tiers of Disc make an excellent companion to either Holy or Shadow.

I would also advise against a Holy/Shadow hybrid because, as you might expect, there's virtually zero synergy between the Holy and Shadow trees.  If you want to be able to DPS and off-heal, you're much better going LOLSmite.  You can do damage on par with a Shadow Priest, though without the nice damage buffs and mana/health regen, and you still have enough talents in Holy to at least have SOME use as a healer, you still have IDS, and you don't have to drop form to start healing.  Only thing is, LOLSmite really isn't feasible until you're around level 60 or higher, because the points you need in each tree to make it work are both fairly deep.