In as so much I had loyalty to any carrier anymore, it was JetBlue. They were different. They still treated you (generally speaking) like a customer not just a number.
Now, they seem like everyone else. I'll no longer book JetBlue just because, I'll truly be booking on lowest fare with an edge (and I can't believe I'm saying this) to WN because they still have free checked bags. I almost always check for my leisure trips and it also seems like the cabin has less fighting over overhead space when people aren't trying to avoid bag fees.
There's little point in me writing to JetBlue, I have minimal points as my new job (that I've been in since 12/2011) has minimal travel and 90+% of my flying is leisure. But, it'll still be a few thousand a year that likely goes elsewhere.
P.S. Southwest has already responded:
http://www.blogsouthwest.com/bags-fly-free-for-all/