Just installed mine and used it in a big Reaper project (44 tracks, tons of plugs) with stellar results. There's a UAD-1 info thread around here that gives one man's optimal Reaper settings for the UAD, which I used.
I think I actually got MORE out of the UAD card than their online cpu-usage chart suggested I would. Don't know if that has anything to do with Reaper's efficiency, but I'm pleased as punch.
And, though it is still early in my experience with it, the UAD stuff sounds simply great.
Spend those 14-day demos wisely! I made the strategic mistake of breaking open the Precision EQ and Precision Limiter demos to master the aforementioned song--with outstanding results!--but I have nothing else even near the mastering stage at the moment, so the days are ticking away and the demos lying unused...