So I've been tanking end game content for about 2 weeks now (tanked ICC 10 8 days after I dinged woot!) and my talent spec only uses one point in guarded by the light for two reasons mainly, I personally have never seen the mana gain tick while I had two points in the talents, and I like a little more raid utility with having Divine Sacrifice in the mix (while OT'ing in a heavy raid damage fight, that 30% shield wall makes things easier on the healers).
Because I don't have enough posts to link things I'll just paste the tags after wowhead.com
Talent Spec:
talent#sZE0tA0ugGsIuszEb
Guarded by the Light per wowhead:
spell=53585