This short article details how Microsoft in their Form 10k filling has detailed that certain Linux distributions could become a "threat" going forward to their desktop business.
Red Hat and Canonical are the named business that could become the threat and it steams mainly from the new Netbook market that has developed over the last 2 years.
Does this show that Linux use on the desktop is increasing? Maybe, maybe not. Maybe it's just a sign that more business users are using it and that Linux is finally being shipped by OTMs. Either way it is an encouraging sign.