Despite being billed as a "multi-region" player, the unit I received was locked to region 1 and had to be unlocked. The process was simple enough, but I should've been spared the effort and received what I'd paid for.
That aside, this somewhat infamously problematic player (which explains all the refurbs) has worked well for us ? and in particular, our young children. We've been able to play all the region 2 DVDs sent by the grandparents overseas, not to mention the region 1s we already own. (That region-locking even exists anymore is a bit of a farce, but I suppose this isn't the appropriate forum for that gripe.)
Two FAT-32 formatted USB sticks (2GB, 4GB) have worked well in the USB slot; the only time I had problems was when I formatted a stick in FAT-32 in OS X and not XP. I've been converting the recordings on our DVR to DivX or XviD format, and so far all of them have played without complications. I wish there were support for more codecs and a better file browser, but perhaps that's nitpicking. Incidentally, the player also boasts a "Windows Media" logo, but I haven't had the courage or inclination to try out our video files in the Borg's proprietary format.
What the DVP5990/37x boils down to is a decent player that can handle any DVD and any DivX-formatted media file. Which is pretty handy if you don't want to invest all the time and money in a home network/media server-type setup. And it's even possible to flash these players with custom firmware to give them a few more features and remove some of Philips' lamebrained limitations, such as max. 14-character filenames.