I think all of the arguments about DJs playing with CD-Rs, MP3s, 8-Tracks... whatever... is total nonsense and probably comes from the kids who sit there and wank over the newest issue of Future Music and have probably never actually DJed on any sort of regular basis to a real crowd in a real club.
It's all about having a solid, portable, and reliable way to play the music that the crowd wants to hear and not lose too much money or break your back in the process.
If lugging around 300 lbs of records works for you and you're not worried about some asshole stealing your stuff when you go to take a piss or get a rink, be my guest.
I own almost 1000 records and about 4000 CDs. I can not tell you how many CDs I have scratched, lost, had stolen, had drinks spilled on them, etc.
If you're more worried about how cool you look rather than how good of a DJ you are, you're a putz and probably won't be paid very well or be a DJ at any notable club for a very long period of time.
If you can find a club in NYC anymore that has working 1200s, I'd pay you. Hell, most of these places barely have the shitty-level Denon soft button CD decks still. It's a joke.
I don't like to spin off of a laptop, but it's the smartest way to go in terms of how much music you can bring with you and portability. Also, since promoters think that having like 10 DJs in a 4-hour night is a good idea, rather than having 1 or 2 good DJs, it is the easiest way to get in, hook up and break straight down after your set.