Interesting counterpoint: I've had an HTC Desire on Vodafone for a while now and the missus just got hers today. Since I got it, on contract mind you, it has not once actually flashed a vodafone logo at me. Furthermore (despite the hoohah vodafone caused with their *not really an upgrade* software upgrade) I've not got any vodafone 360 shovelware on my device and never have.
In addition to this, the missus' sim doesn't go live until tomorrow and while I was copying the contacts over by putting her pay as you go O2 sim into it, I found I was able to make calls with the O2 sim in the Desire. I don't know if this means that the handset is completely unlocked, or if it's just pre pay sims that work, but it made me smile.
Just thought I'd raise these points, not really in favour of carriers as I'm fairly sure they're all bastards, but it seems like vodafone at least didn't go the whole hog in the bastard contest for this particular handset.
YMMV and all that.