I used Media Monkey to sync 14 GB worth of MP3 files to my N900 form my old Itunes library.

The player works pretty good, my main problem is Media Monkey not keeping all the albums together because of it's translation of the ID3 tags.

I can't say if it's the player or the Media Monkey sync, but my N900's album view is missing alot of album art, but when you play the individual tracks, the art appears just fine.

The player itself is responsive, and offer a very quick search just by typing anywhere in the app to bring up results just like searching contacts from the desktop.

Shuffle works probably just as fast as an iPod, even with 14GB of music to shuffle through.

Playlist creation isn't really intuitive, but it can be done on the fly in the application without having to create them on a desktop and sync them over.