I have Atonement spec, and I've found a use for Smite/Holy Fire, in every fight, except Ragnaros, which our raid has just started on, in the last couple of days, so still mostly trying to figure out where to not stand, so far! ;>)
Reading Sebadoh's post, it struck me that I've been doing pretty much what he describes, for each fight. There seems to be opportunity, in each fight, for me to use Smite/Hoy Fire, even if only briefly enough to stack Evangelism. Plus, it's a great way to conserve mana, for when it's needed. I can't stand using Heal, because it's slow, and it's a pretty small heal, for all that casting time. The offensive/heal aspect of Smite/Holy Fire is just so satisfying...once I figure out how my tank's health is going to spike, or not, I can use this mechanic, while having bubble/penance/GH ready, if needed.
I have to admit, it took a while to get a feel for that timing, with a few, "oops, got that GH off too slowly" moments.
On a minor note, the spec is just plain fun, in Heroics, too...er, 5-mans, that is...haven't done Heroic raids, yet. That may require taking a serious look at the alternate spec.
Please, take this with a grain of salt, as I've never even tried the alternate spec, since Cata started.
BTW, my raid leader originally wanted me to spec Holy, but I sorta talked him out of it...
-"Just like a buzzin' fly, I come into your life, I'll float away, like honey in the sun..."--Tim Buckley