Since this thread has revived...I wish to God Delta would actually train its agents on pets in cabin. It's not like they're an extreme rarity, but 60% of the time I get an agent who acts like they've never seen one before. This last one managed to (accidentally, I'm sure!) keep my dog's rabies certificate after checking it, and (despite the efforts of several kind agents and one truly nasty one I had to leave a complaint on) I ended up missing that flight. I'm not mad about it (I should've double-checked as I walked away from the check-in desk), but people predictably screw up unfamiliar processes.

Delta also recently jacked up the fee to $150 each way, which is pure profiteering. There are zero services provided for pets in cabin and they replace your carry-on so it's not even a weight issue.