Well Zen,
I see the normally chatty bunch has abandoned you, so I'm gonna try and help out. I do NOT own a Sig, because I'm left handed, and the hammer drop is ETERNALLY right handed. But I do own an H&K USP45. I lusted after it BEFORE they even had a .45. All they had were 9mm $ .40, but I just knew that HK wouldn't let me down.
Anyway, I've had it for about 5 years now, and...
I LOVE IT!! I LOVE IT! I LOVE IT!
Now, having said that, I'll elaborate. It has never malfunctioned on me even ONCE! It is much more accurate that I am. If I do my part, I WILL hit what I'm aiming at. I can fire it even better one handed. Recoil is moderate, and completely controllable. I could carry cocked and locked if I wanted. It has a UTL attached. It holds 10 rounds of big bad .45+P.
Now to the down side...
It's big. No, I mean BIG! And it's WIDE. The trigger's a bit heavy on DA, but single action is BEAUTIFUL! I would say it's heavy, but so is the Sig, so I won't. Did I mention it's wide? I mean this is a BIG darned gun! If you don't wear at least LARGE gloves, I'd look twice. Maybe the USP Compact? Anyway, you get my point. It's like Rosie O'Donnell WIDE!
Honestly, I ALMOST traded a fellow TFL'er my USP45 for a USP45Compact because of the size, but I changed my mind at the last SECOND (sorry Jeff!)
I wanted to have a gun for the house and the hip, but I decided to keep the USP for the house and get something new for the hip.
I'll tell you what everyone told me when I almost traded. Find a range that rents pistols. Shoot them both. You'll figure out the rest yourself. They are both great guns and 100% reliable. You can't go wrong either way. You just gotta figure out what fits you.
Hope I helped, and hope you didn't fall asleep from reading all this!