My attitude is that Glock vs. HK USP is a tossup in many cases. Both have a lot of strengths and very few weaknesses. I know USPs are more expensive, but I think they are worth it. It really boils down to which one a person shoots best and which trigger system works. If your friend likes Glock triggers, he might look into the LEM for a USP, though I haven't heard much about it since the INS contract.
But in .40 I definitely would prefer a USP over Glock. I know Glock .40s are incredibly popular with law enforcement, but the kB/unsupported chamber thing makes me nervous. So much so that I refuse to shoot anything other than ProLoad in my Glock .40.
My livelihood is dependent on my hands. I want to minimize the chances of anything blowing up in them. Yes, I know I'm being paranoid.
USP fans will quickly point out the USP was designed for the .40 first. It is not a "scaled-up" 9mm. Does it seriously make a difference? I think it does, but I can't offer any conclusive evidence.
And, as a USP fan, I'll offer my opinion that the USP's individual parts are more robust than the Glock's. Of course, the Glock fan in me will quickly point out I can easily detail-strip a Glock and replace any worn/broken parts in minutes.
I have shot a friend's USP compact .40 and, frankly, I preferred it to the Glock .40. It also was more accurate in my hands. That is probably subjective, though, as I seem to shoot USPs a little better overall.
Dry-firing may be a bit of a question mark. Latest I've heard is the problem was caused by brittle firing pins a few years back. New models are supposed to be better. I've dry-fired my 2000 USP a few times with no ill effects so far but I use an AZoom snap cap when I'm doing an actual dry-fire practice session. Paranoia again.