This came up on here a couple months ago when Delta announced that they were going to allow you to check a bike for the price of a regular bag. I don't know if anyone has posted an experience, so thought I'd share.
Last week I flew Delta to Boston and took the bike. I packed the bike in a box I got from Peddlers. The Transition box is bigger than others I've used so packing was easier, and it still met the dimensional requirement of L+H+W<115". Weight limit is 50lbs, which I didn't think would be a problem, but my Smuggler+helmet+camelbak+box came in right at 50lbs.
Leaving Austin, initially we tried to go to the skycap, because who wants to drag these big ass boxes inside, but he doesn't work for Delta and had no idea about the new policy. So, we dragged the big ass boxes inside. We got lucky at the counter and the first agent that was available knew about the policy and checked us in without any problems. We then dragged the big ass boxes over to the oversized baggage area and we were good.
Returning from Boston, we skipped the skycap and went straight inside. After dealing with some logistical differences in the check-in process, we got to the front of the line and had one agent yelling at us "You can't check that, those are oversized, we don't take bicycles, you can't cut line" (she was actually working with another customer and just chose to share her opinions). The next agent that opened up (thankfully not bitchy lady) hadn't heard about the policy but he listened to our explanation and pulled up the policy. After that he was very friendly and checked the bags for us. We took them over to oversized baggage and all went well.
A couple of notes -
1) In both directions TSA cut open the boxes to verify the contents. Nothing was missing and they actually did a better job taping up the boxes than I did. But be aware, that is not the place to stash your weed.
2) It should go without saying, but make sure the guy picking you up at the other end has enough space for bike boxes and passengers. We had measured beforehand but it was still a really tight fit and I'm pretty sure the passenger in the back with the bikes was not traveling legally.
Finally, I highly recommend the riding around the Boston area and Kingdom Trails in East Burke, VT. It was an amazing week of riding!