Well, I have to admit I'm considering getting a Boxee box, and I'm in the UK.
While Boxee does actually play iPlayer (reasonably well, integrates with tv shows library or there's an app), I'll agree that tv show streaming in the UK generally is atrocious.
Netflix are rumoured to be in the UK for the end of the year, and Hulu too, but of course noone can count on either until they're actually here..
So, why a Boxee box? for playing back local media. It's the one interface I've found that my family can actually use without getting frustrated - I like viewing our photos on the big screen, and we've got a small flat so I don't like having loads of shelves taken up with DVDs, so rip them all..
So for local media, or photos, Boxee is fantastic, but I'll agree with you that online sources so far are limited. I suppose by buying one I'm betting on the future, in the hope that Spotify integration improves, Netflix / Hulu comes, or it can integrate Project Canvas..
All I know is that when these services do roll around, my money is on Boxee just because it has the best interface, usable by everyone.
Macbook Pro (2009) | OS OSX 10.6.4 | CPU 2.53 GHz Intel Core 2 Duo | Video NVIDIA GeForce 9400M | Version - 0.9.23.15885
Boxee Box (2010) - 18.104.22.16843