Saw one in the funstore the other day, and played with it for a bit.  First HK USP I've been really impressed with the ergos of, I really like the way the pistol felt in my hand.  I've been trying to convince myself for years that I need to get a USP Tac, I think this may be the one for me.  Can anyone attest to the accuracy vs. the standard USP45C?  How hard is it to add night sights?  The only concern I noticed was the DA trigger pull was long and tough.  I'd carry it condition 1 for the most part, and the SA pull was fine, like my Sigs for the most part.  Anyone's thougths or experiences would be appreciated!  

The ONLY difference between the Compact .45 and the Compact Tactical is the barrel.  Same frame, same mags, same slide, same sights, same trigger.  It will NOT be more accurate than a normal Compact.  The o-ring is supposed to make it more accurate but only if shot out of a machine rest.  In human hands you will not see any difference between an o-ringed barrel and a non-o-ringed one.
I made a CT clone before the CT hit the civilian market with a Jarvis barrel.  It was not o-ringed.  It was as accurate as any HK barrel, but since the CT had an o-ring, I sent the barrel back to Jarvis and had an o-ring cut into it.  Guess what, just as I suspected, no change in accuracy.  The HK (and Jarvis) barrels already are more accurate than the shooter so adding an o-ring is not going to help anything.
Remember, only the first shot is going to be DA and you get use to it soon enough.  Personally I like the V1 and carry hammer down, safety on and do the first shot DA.  I don't have a problem with it and I doubt you will either after shooting it a bit.

It is no harder to add night sights to an HK than it is for any other pistol.  If you want to shoot a can you will need taller ones and HK is about to bring out the CT with tall sights like the prototype had,and they may be night sights.
The prototype used Heinie Compact Tactical tall night sights and that is what I put on my clone.  They are fine and shoot very well.  Just push out the old, push in the new.  Done.