So I did a post on Tanking as Holy. I thought I did a pretty good job and I'm sure it was helpful.
I was reading Banana Shoulders and read his post today on Holy Tanking. The advantage he has is that he is actually a Holy Paladin, who has done some Tanking in Holy spec. It is always good to hear it from someone who has actually done it, in addition to the perspective of one who can theorize about it.
If you are Holy, and want/need to do a little Tanking, give it a read.