I bit the bullet and went Holy. 47/14/0, to be precise. It started off as 41/14/0, and then I couldn't figure out where to put the remaining points, so I decided to try out Blessed Life. Not sure if Blessed Life is really helping, but it seems good enough. The build is pretty good for healing, I find.
Since then I've main-healed Sethekk Halls, Durnholde, and Shadow Labyrinth. I think this was a good decision, if only because I haven't seen a priest or druid yet. As far as healing difficulty goes, I think the increased health available in TBC has really helped the paladin healer. You seem to have a lot more time to react, to cast Holy Light. Before TBC, I almost never cast Holy Light, as the target would usually die before the cast finished. But now, thanks to the 2 second Holy Light talent and the increased health, it's actually a useful spell again.
Speaking of talents, the 41-point Holy talent, Divine Illumination, is very strong. It's not a stylish 41-pointer, like Crusader Strike or Avenger's Shield, but it is incredibly useful. I try to pop it often, at around the 70% mana mark, and then go to town with Holy Light. Indeed, I think that builds that only put 40 points into Holy are shortchanging themselves if they want to be healers.
Of course, paladin healing is very group dependent. I had an awesome group for Shadow Labyrinth, probably the best pick-up group I've been in, and that made it much easier to heal. With a worse group, I could easily see Shadow Labyrinth being hard to heal.
The other advantage of being the only healer is that you get all the healing loot that drops. I've picked up four or so blues for my healing set. Sadly, I'm wearing a bit of cloth, leather, and mail, but hopefully I will replace them eventually.
(As an aside, you gotta love tells that begin, "Are you happy with your current guild?" Heh, I guess they liked my healing in Shadow Labyrinth. If I did take them up on the offer, it would probably be a big shock for them when I started meleeing in the raids. ;) )