Rockdoc, I am a DIA traveler myself, and as you can tell by my username, my status used to be with UA. I left UA except for maybe four RT's a year almost three years ago. I now fly F9 as well as HP and have been quite happy. Here's some other things you might be interested in:

-Using the bridge to F9 is almost always more convenient than taking the train. If you fly CO you know what I mean.

-The lines at F9 are shorter, sometimes even shorter than the Premier lines at UA. At other locations like DFW, SFO, LAX, PHX, the lines are never more than two or three people.

-F9's coach seats on the 737's are on a par with UA. Perhaps there is a bit more pitch. Food service is non-existent, which seems to be the rule these days.

-If you end up on one of F9's new A319's, you will find the coach seating the best in the US with the exception of Midwest Express. Great pitch, headrests with wings, foot rests, just a great setup. I don't know why F9 has not advertised these new planes more in the Denver market.

-As far as upgrades, I truly enjoyed getting the bump to First, and as a PremEx it happened frequently, both by the grace of the gate agent and my own purchased upgrades. As a Prem, I found the grace upgrades disappearing and the cert upgrades increasing difficult. If I am going to sit in coach, I would just as soon deal with an airline who seems to genuinely appreciate my business.

I may give UA another shot in a year or so, like Brancatelli says, every airline gets remade on roughly a two year interval. But for now, I am very happy with HP and F9, and when F9 gets their entire fleet changed over to those A319's, they may get all my business.