Thanks for the comment Nick. A couple of points.
QR codes can cope with up to 30% data loss - which should be more than adequate for most use. I'd be interested in seeing what MS can cope with.
Regarding the traffic monitoring - I don't know of a single webmaster who can't install Google analytics or similar. Yes, it's nice to have a ready made interface - but does any website not have tracking on it?
If MS Tags do become successful, I hope the code is opened up sufficiently to allow people to either write their own scanners or run their own servers.