/rant
I personally can't stand WMA, it's a nasty nasty format, even if the audio quality of WMA9 is better than MP3 at a comparable bitrate. I'd much rather go for MP4/AAC or Vorbis (which are on par with or better than WMA9) before letting WMA have it.
Out of all the songs in my digital collection (which is in upwards of 3000 or so), I think only two or three of them are/were WMA at some time. I avoid that format like the plague (I also generally avoid WMVs like the plague, too, and logically, WMA is the only audio format compatible with WMV).
The thing that annoys me the most about WMA (aside from the über-invasive DRM), is the noise that the thing generates. Hit a really high pitch, and the thing squeals like a pig (even at a higher bitrate; at least MPEG Audio has some type of noise dampening system in place, sheesh). I also never bought that claim Microsoft was putting out that a 64kbps WMA (at that point, it was WMA8) is equal in quality to a 128kbps MP3...I tried that comparison for myself, they lie through their teeth to make their format look good.
As for it becoming prevalent...unfortunately, yes, I do see it becoming more prevalent online. I have a simple explanation of it too: people are becoming lazy and don't know p's from q's about encoding audio or video (for those that default to WMV instead of using DivX, XviD or MPEG-1 simply because Windows Movie Maker exports WMV by default - no matter that it has a DV export function *rollseyes*). Not to mention that (as I saw in an article), most non-tech-savvy consumers simply rip their CDs to their hard drive in the native format the player uses (WMA for Windows Media Player 7+, MP4/AAC for iTunes, Vorbis depending on what version of Winamp you use, etc.), and often times think they are ripping to MP3. Even more annoying is that those who do rip to WMA (knowingly or not), often forget (or don't know about it at all) that they didn't disable the DRM option and then wonder why their music won't play when they put it on a different computer.
As a general rule of thumb, I don't even use Windows Media Player 7+. I stick to mplayer2 (Windows Media Player 6.5; you know, the simple interface - comes packaged with all Windows platforms since the mid-90s) and Media Player Classic for my video needs, and Winamp 2.95 (just recently upgraded from 2.81) to play all my audio. I do keep the newest set of Windows Media codecs on my system though, just for the sake of being able to play newer files. I just don't let the defaults take over.
/rant
Whew. I feel so much better now that that's off my chest.