If so, how does it compare to the standard Windows player? Is it worth the investment? Can it play mp3 files in formats other than 128kbps?

I was using withMP3 on my Maestro before the Axim. I found that it worked well. One difference between it and WMP was that withMP3 came with a 10 band equalizer. withMP3 was also able to play any bitrate I had from 64-160, including VBR files.

The only issue I had with it was that I initially installed it to a storage card, which was a big mistake. It repeatedly locked the machine until a soft reset.

I would say it would be a decent choice in a nice world of choices (PocketMusic, WMP, PocketMVP, etc.)

When the Naysayer talks with a voice like ice cream
Reason blows away like so much dust
- Temple of Low Men

I play mp3's on mine all the time (no need to keep buying batteries). Windows media player was ok, but I noticed it wouldn't play some of my mp3's for some reason. I use pocketMVP now and it is much better, I've been able to play all my mp3's. Plus there's a lot of features in PocketMVP that I like such as:

Being able to turn off screen, so I can put my axim in my pocket
Programmable hardware buttons
10-band equalizer
Uses less processor, so it's faster and batteries last longer

-Gabe