I found even as a holy pally it was tough to heal a lot of stuff in heroics, because you pretty much can only focus on the tank until you have a bunch of healing epics. but by then heroics are useless for you unless you just want badges to build up an alternate set. A lot of stuff in WoW, especially raids/heroics, seems designed largely around having one class/spec to counter the fight.
like the time I had good success in heroic MT with my pally, we had ranged dps for the first boss, along with an enhance shaman and a tank with an insane shadow resist set.
and I read that whole freaking priest thread and all I can say is the guy has good opinions, but man is it long-winded and full of the insane number-crunching that blizzard fans always do to the point that it sucks the fun out of everything. I agree with him saying holy pallies are the antithesis of fun, though. they are just boring to play altogether because healing is all about 2 spells and refreshing buffs, and it feels very controlled and pointless because nobody should die unless the dps/cc fucks up and lets stuff get out of hand. and when you aren't healing a group you're going to get bored if you solo grind anything, though maybe that's better in 2.3 (probably not).
I still feel like the paladin is a lame class overall, but it's just that they do nothing cool, unless you like seeing big numbers pop up infrequently. they aren't a crap class, but they kind of remind me of Medic in TF2. except in TF2 when you run around healing someone you can still have fun dodging attackers coming after you.
that's why if I was going to play a healer I would pick priest/shaman (easiest to synthesize gear so you can heal and solo dps, even if talents don't stack/aren't readily available for both) first, then druid (for all the swiss army knife utility) and last, paladin. I had more fun, pug stupidities aside, playing my paladin as prot. but it was tough to get past the WoW userbase stigma against prot paladins, and on the server where my pally is, my other friends played a super-geared feral druid, a super-geared enhance shaman, and a rogue. so the real best role for me was boring healbot.
tl;dr version: If you could set autofollow distance to ~35 yards behind a target, macro your buff refreshes and the pathing let you genuinely follow someone through an instance, you could bot a pally just by following the tank and putting a bobbing bird on your holy light/flash of light hotkey.