Okay, so I've been waiting on the sidelines, reading all the pro/con posts about USNightmare, and here's my story...
I was a Gold Preferred Dividend Miles customer on that airline, having been loyal since the time of the Republic Airlines merger. However, I've experienced exceeding poor service all too often with them. There's a billboard along I-95 in front of PHL stating how their employees are fed-up with that company, and now that sentiment has flowed over to this once-loyal customer.
Two examples of the latest experiences with USNightmare:

Having to fly R/T from PHL to PVD weekly for 10 weeks, USNightmare lost my luggage 6 times Northbound, and 4 times Southbound. All flights were non-stop on USNightmare equipment. For a week-long trip (Sunday night to Friday night), my luggage took an average of 2 days to find its way to me. I was never offered any complimentary shaving kit, or anything else for my inconvenience. (Yeah, I know....they don't have to offer beans. However consider possibly doing the "right thing" for a customer.)

My wife is taking me on an Alaskan cruise vacation to celebrate my birthday this May. Having made our flight arrangements apart from the cruise ressie, she booked flights accomodating not only our business schedules, but that of the cruise as well. Everything was booked, and we would have enough time for some sightseeing in Alaska prior to the cruise...until USNightmare decided to change their schedule.
Incredibly, USNightmare rebooked us onto an outbound flight scheduled to arrive
after the cruise departed...
without notifying us. (I simply happened to check our ressie on-line.) When calling their "customer service" number (and reaching an off-shore call center), I was told there was nothing USNightmare could do for me. Even when I pointed out USNightmare policy is to allow 72 hours for me to accept or decline the flight changes (something USNighmare
did not do), the conversation turned to cold indifference on the call center's part. I escalated to a Manager, who was
more rude than the call center agent. He told me he would (not could...would) do nothing, he spoke over me at every opportunity, and when I asked to be connected with his supervision he became even more rude. After a lot of back-and-forth, the call center manager finally offered to refund my money in-full. However, this would leave me with the only option of rebooking on another airline with higher ticket costs (about $400.00 more for two people).
(Having said this, allow me to point out to the gentle readers of my post, I realize call center agents, their management, ticket agents, gate agents, flight attendant personnel, pilots, et cetera, hold the key to a smooth relationship with an airline. In other words, you simply don't purposefully try to anger them. So, I was very professional in all my dealings with the call center personnel.)
USNightmare did not follow their 72-hour rule, I got my money back but I had to pay the difference for a competitor's tickets (..a competitor who USNightmare code-shares with).
I will never give my business to USNightmare in the future. There are other examples of how this airline has gotten terrible, but I'm already off-Disney-topic (sorry moderators!).
Thank you for allowing me to vent..... ah, I feel better already...