I've had 2 DKs in the past week queue in as DPS while in Blood spec. Once while I was tanking, once while I was healing. Yeayeayea, it was a normal, but still, it's 10G to dual spec.

The first time I noticed as soon as I zoned in. I wasn't trying to be a jerk about it, but I asked the DK if he was going to swap specs. No response. So I ask again and he pops into Frost presence. I look at the healer's gear and comment that "No, I mean switching to Frost or Unholy since you're a DPS." The response I got back was "I haven't had time to figure out a spec." So my next question (which I thought was valid) was: "If you're blood, why aren't you queuing as a tank?" Dude got so annoyed that I was trying to figure out why he'd wait on a DPS queue with a tank spec/not have a DPS spec that he finally says "It's a normal, jeez. Screw this." and he drops group. Which was fine for me--the healer shouldn't be having to heal 2 people who are going to be fighting for threat.

I noticed the same in another instance while healing. "DK, why are you Blood spec?" "Sometimes I like to tank." "Okkkay...but you're not tanking this run?" DK (and an Arms warrior), decide that their tank is moving too slow and pull a boss before the tank was ready. That was a blast to heal and I felt bad for the tank who spent the entire fight trying to grab aggro from the DK.

I finished out Twilight Highlands and Uldum with decent enough gear for 3 specs to be successful. I'm still healing in random instance and quest rewards without issue (normals at this time). I don't see how it's so hard for people to put together a second set of gear for their "other" role.