My opinion
Well, as someone who has owned a 7mm Remington Magnum, but has never owned or fired, or even handled a 7mm Remington Ultra Magnum, here is my opinion.
TOO DAMN MUCH.
Too Much Noise, Too much blast, too much recoil, and if you buy factory ammo, too much money.
Yes, the ballistics do look impressive, but...(and don't flame me), it's still just a .284 bullet, no matter how fast you move it. I am still not going to use a 7mm Ultra Mag in a situation that I feel calls for a .375(big bear in Alaska for example)
I loved my 7mm Rem Mag for deer and elk, and I want to get another one. But, if I can't find a 7mm Rem Mag, there are about 10 other calibers I would get before thinking of gettting a 7mm Ultra Mag.
So, if it was me, it would go in the trade/sell catagory.
But, that's just me, and maybe I'm a wimp.
greg