Microsoft did not build its empire by conquering the server market back in the 1990s. It built its empire by capitalizing on Apple's colossal stupidity and greed which opened the door and laid out the welcome mat for Microsoft to dominate the home and office desktop.The market for servers is much smaller than that of home and office, yet Microsoft is making inroads there, doubtless helped by the fact that the people controlling the purse strings know Microsoft products. Linux? Unix? *nix is the unknown, and people prefer to use what they understand.
If Linux is to start giving Windows some badly needed serious competition, a desktop distribution as robust, full featured, and as easy to use as Windows XP or Mac OS X needs to come to market.
Or, to put it in Jane User terms: As an end user, I can't tell and don't care if a server runs IIS, Solaris, AIX, OS X Server, BSD, or Linux. The pages served look the same. I do care if I can use my desktop computer to accomplish my daily tasks swiftly and easily.