I've commented before about tanking with my DK in 5-man heroics with my dps spec (preferably blood) and tank gear. It's fun, fast, and .... fun!
The last few days I've been running chain heroics, trying to help guildies get Glory of the Hero achievements, and collecting badges for my enhancement offset.
Generally, I've had a guildie tanking, which means we vastly, vastly overgear it.
So far, when I've healed the runs, I've still been in resto spec, with resto gear.
It's been very fun, though, to keep Earth Shield on the tank, occasionally riptide, and toss a chain heal in there once in a while, and then dps. I've been dropping magma totem, and then stepping back to toss a few flame shocks, lava bursts, and lightning/chain lightning out there. Nothing amazing, but given that ~700-1000 healing per second is all that's needed, I've been able to top 1000 dps sustained with my healer on these runs. Fun stuff!
I think I'll have to drag a couple of pieces of elemental gear with hit on it out of my bank and equip them for heroic 5 mans to allow me to combine healing and dps better!
I'm sure some of you out there have experimented more extensively with such shenanigans, but for now let me tell you, it's a blast! ;)