I now have had enough time with my new Mossberg 835 Ulti-Mag that I feel comfortable sharing a range report. I have run about 200 rounds of 2.75" and 3" 12 gauge shells hrough it and have had no problems. I have shot clays and birds with it and it loads, shoots and ejects without issue. Despite what you hear about the "rattling" of Mossbergs I have not experienced that with this model. Its a tight gun (some of that is because its new) and seems to be well designed.
I am also impressed with the lack of recoil (much due to the ported barrel) and the weight of the gun which is lighter than most 12 gauges. In fact the felt recoil is no more than my 20 gauge using 2.75" and 3" shells. I have not run the 3.5" shells through it yet but plan to in the future to see how the gun performs. I do a lot of bird hunting and feel very comfortable with the gun even in upland hunting situations. Its certainly not a very light gun like a 20/28 gauge so if you do a lot of upland walking this may not be the optimal choice, but for the typical pheasant hunt (out in the field for a few hours) it is not taxing to carry.
Overall this is a great all around bird gun from ducks to quail to turkey. I carried it recently in some pretty cool temps (teens) and no jam ups. If you are in the market for a great 12 gauge at a decent price ($449) this just might fill the slot.