Windows Vista is finally out and along with that Microsoft seems to have kick-started its Vista-Live joint initiative. This initiative aims to push Microsoft's new web properties in tandem with their dominant Windows operating system - and so become a leader in the web industry as well. Basically this means that Microsoft makes its Windows Live web properties the default in Windows Vista PCs, where possible - for example Live Search is the default search engine in IE7 on new Vista machines. 

Measuring Vista's impact on Microsoft web properties 

Live.com:

MSN.com: 

Measuring Vista's impact on Google web properties 

As a final note, Alexa competitor Compete's results are in parallel with ours. According to Compete, these giants all have an increasing trend in page views, but Google's slope is apparently lower than those of MSN and Live.