Regarding the popularity issue, I agree with WestDocs... it's growing and will get larger.
When you look at the resources Microsoft used for integration of SharePoint 2007 with MS Office 2007, you can see a bit of their crystal ball strategy. I've been telling people that if you own MS Office 2007 in an enterprise environment and are not using SharePoint 2007, you are wasting a major piece of functionality within MS Office.
I am betting that most corporations using MS Office and Exchange will eventually roll over to SharePoint.
Regards,
Mark