They're the standard nowdays and there's nothing unprofessional about it. More and more people use USB keys and hard drives on the CDJ2000(850, 900, and from other brands as well) as burning cds is "stupid". There's also more and more people doing DVS with their computers and also through their cdjs as with HID integration you can use the cdj to control your computer directly(rekordbox, traktor, Serato...). Tons of options ;)
The new generation CDJ have USB input :p, that is the CDJ-400, CDJ-350, CDJ-850, CDJ-900 and the CDJ-2000. The CDJ-400 is still part of the not-rekordbox generation, so i do not recommend it! For starters the 350 is awesome! If you are more experienced i would go for the 900's (because of the Link feature), not the 850's! For pro's definitely go for the 2000's, they have Link, Cuepoints, better screen, just the best device around!