SharePoint is absolutely dominating among US government agencies.
I lived in three countries in europe, and I've met people working on sharepoint in all three, so add another anecdotical evidence on this side of the pond too.
I suspect that ghurlman means that Microsoft SharePoint Workspace product (based on Groove) isn't as popular as the very succesful SharePoint server - I don't think the latter has much Groove-derived technology in it (although I could well be wrong).
SharePoint Server and Groove only share enough code to make the Workspace product work.
SharePoint is fine. A rather large portion of my income depends on it.
SharePoint Workspace, which is what Groove became is never used, anywhere.