Back on Union, my Regeneration Stalker before she became Incarnate. Mainly because I didn't constantly run ahead and leave the group behind during Task/Strike Forces, choosing instead to AS the stragglers who didn't get caught in the AoE control (with a particular focus on healers, although that didn't get noticed very often.)
I also got complimented on my tanking during my 1st Hamidon raid. I was only the reserve tanker for the main core, and I eventually faceplanted because I wasn't paying attention to my inspiration status when I actually went in, but I think I was the only casualty in the whole raid.
The only other time that comes to mind wasn't on CoH, but Star Wars: The Old Republic. One of the low level missions with a Bounty Hunter, I accidentally agggro'd several groups of mobs. Fortunately, half of the early powers for the class are AoE knockdowns, so I was blasting 1 group, targeting the next and firing off a few basic shots, blasting another group, etc. Halfway through, I noticed another player just standing nearby watching me. When the mobs were all dead, he said "Wow! You're really good." I almost replied "It's because of all the legacy buffs from my other characters on the server" when I remembered that this was the first character on a new server, and didn't have any of those extra buffs. I really WAS that good.