I'm with you. I think Linux is doing a great job of knocking MS off the server market. However, it is doing a much better job of knocking SCO Unix and other small platform Unixs from the market. MS was not that big a player in the server market to begin with. So far, though, it looks like MS is holding it's own on market share. I expect that to change in the coming months and years, but not drastically. It will take time.
Contributions to the current change are based mainly on MS XP price and pricing structure. If MS does nothing, MS will not continue to grow in the server market.
The biggest hinderence currently for Linux in the server farm is Linux on the desktop. Having a great server tool is hampered by having a lame desktop. I have only used KDE and it has a lot of growing up to do. Currently I prefer to telnet into Linux and work from the command line rather than trying to fight with KDE.