To me it seems USB burners fall between IDE and Scsi. They have the drawbacks and plusses of USB w/o all the problems OF IDE. I've heard that you can use your computer while burning. I haven't tried. My Mitsumi operates in win 98 as a virtual scsi device. I have never seen anyone who actually has one, say anything bad about 'em.
You don't have to worry about what IDE channel to plug into, or how to arrange everything for optimal performance. You just plug it in and it works. New software supports them, Adaptec recognizes mine as a mitsumi IDE drive. HEll my girlfriend uses it as a cd player, while she works on the computer.