I've seen what Microsoft has done with Longhorn and a lot of people will be attracted to it for the Eye Candy. Heck I am. I love OS X don't get me wrong.
Windows is starting to take the look of SLED 10 (SuSE Linux Enterprise Desktop 10) with the integrated search (not sure if anyone else went to Brainshare) kind of like Beagle, the Window look of Gnome, Transparency. Mac OS X features or semi-features such as the Window listing, etc. Every company does it.
Right now I've settled with the OS's I've used. If I buy a PC I know I'll use it for gaming, if I buy a Mac I'll use it how I've always used it - graphics, layouts, etc. (I'm a bad artist, layout person, etc., but I have a Mac so it looks good *thumbs up*). OS's will just provide what users need out of them. Linux has tons and tons of opensource items - that's good. Mac's have a unique and simplistic interface - e.g. the Dock, the Menu bar, etc. Windows has tons of games.
You may see me buying a PC down the road probably just for gaming. I can't wait to see what OS X Leopard brings, but each OS has its flaws, each OS has its ups and downs, just look at what you need. I'm going to stop flaming Microsoft and Linux because for my needs, they get the job done, but Mac OS X is my Power Machine - Exposé, the dock, terminal, etc.
EDIT: A lot of the stuff we say - Leopard should do this, Leopard should do that, Linux did (alt-tab preview)--again this was at brainshare for SLED 10--, Microsoft used, and Apple is still a coin toss.