One of the main reasons I prefer Windows Media Player to iTunes is that WMP monitors folders and automatically updates your library. In other words, if you add or remove folders on your hard drive, the changes are reflected in your library - automatically. For some inexplicable reason, iTunes doesn't do this. I had been using a wonderful little product called iTunes Library Updater to "fix" the library, but it's a manual process and one that really started to grate on me.
While I really liked some of the new interface and features in Windows Media Player 11, the first beta was just too damn slow - but Beta 2 is MUCH, MUCH faster. The instant search works well, and the video interface is very nice and clean. The integrated Windows Media Connect is also a nice touch.
People are raving about the changes in iTunes 7, so I decided to give it a go with my new 2nd generation nano. Paul calls it "the best software-based media jukebox [he's] ever used." The first thing I noticed is that they finally added an auto-update feature that (appears) not to require a full download for incremental updates. And at first glance, the interface does look nice. I particularly like some of the additional views for managing attached iPods and stats on what is taking up the space.
iTunes 6 was a little sluggish at times, but iTunes 7 is EXCRUCIATINGLY SLOW. When I say slow, I mean ... like.. 5-10 seconds when clicking on a different genre in the browser. And there are a number of funky bugs in the display, where fonts revert to defaults and portions of the screen stop repainting (I tried to get other shots but it seems to happen mostly when the machine is hung). Re-installation improved the experience somewhat, but it's still a bit laggy.
Maybe iTunes is better on Mac OS X, but Microsoft definitely has them beat on Windows... for now.