I commend DPS when they do things like:

Ranged physical gives TP or MP restoration when respective bars are low
Goad is given
Appropriately using AoE skills

Usually only commend a tank if they don't stop. I don't care about large or small pulls, just don't stop. I get tired of hearing my husband complain about the tank stopping and making him lose grease. Keeping aggro is a given, too.

Healers I'll commend if the DPS or tank didn't fulfill those requirements and they at least tried to DPS. Or didn't go DPS crazy and got us wiped from forgetting to heal the tank (that's becoming absurdly common). Yeah, I rarely commend healers.

Most of the time, I end up giving no commendations out.