Ah, Young Grasshopper...
If you had started in the I/T field 25 years ago when the dominant players were IBM OS2, Novell Netware, WordPerfect & Lotus, everyone was doing development with Borland tools and no one ran critical business apps on anything but a mainframe you would show a little more wisdom instead of blind hate for anything Microsoft.
Yes, MS has entered a few markets only to flounder, fail and pull out. But they have had just as many where they went from upstart to dominant player - through innovation, aquisition or just plain determination to keep improving until they came out on top. And lets not forget that Apple did not invent the GUI, the MP3 player, the smart phone or the idea of a small tablet computer. Much like Microsoft they saw an market niche with potential growth and tried to make a better product. Competition is good.
Will the Zune, Windows 7 phone or XBox dominate or fade away? No way to be sure, but I wouldn't be scheduling any dances on Microsoft's grave just yet.