I use mainly the internal player (S60v3), but occasionally flip over to OggPlay once in a while -- the built in one works. *shrug* I would welcome a much better one -- I tried XSound but didn't like it at all.
I drag & drop -- I have beyond gigglebytes of DJ mixes from many years, usually ~120meg in size MP3. They're loosely organized on a remote diskage that's plugged into a laptop that feeds into the stereo system, with 'mpd' (http://www.musicpd.org/) and a webUI to control it. So, desktop management is more of a hinderance than a help -- I just jack the phone in, reach across the network and drop whatever I feel like listening to for the next few days onto the microSD.
On a 2gig micro with .5 used for apps, I'll get maybe.... 12? good sized mixes on there and a handful of MP3 singles (or less if I throw a couple videos on the card).