Yeah well the other day I got me one of those shiny modern MP3 player thingies — namely a Sansa Clip+. Really nice gadget and all but whenever I copied some of my OGGs on it it would hang during the library update.
Long story short after two days of tinkering I found out Mac OS X creates ._somefile files if the file system copied to doesn't support all required attributes. The whole concept is called Apple Double Format and frankly not including an option to turn it off in some way seems totally ridiculous.
Though it seems Apple does indeed know how stupid the concept is since they provide the dot_clean command.
In case your Sansa MP3 player hangs up after putting music on it this hint might save you some pulled out hair.