I have just purchased a macbook and made the leap from vinyl to DJing with a computer, and am using DJ 1800. First a bit of perspective.... I am not a professional DJ but have been DJing for fun for 10years or so - beat mixing mainly house music at parties and the occasional clubs and bars. I also should point out that I have nothing to do with DJ 1800 other than using it - so i offer this review from an independant perspective.
Having read the reviews here, I had some reservations when I did take the plunge, so I thought it would be useful for me to go through these reservations incase someone else is thinking the way I was.
You can beat mix using a laptop, connector cables and a imic to connect your headphones. There is no lag when running the master output through an regular line-in amp and the cue through an imic.
Yes, you can use iTunes as the playlist manager, so no, you don't have to go through any hassley playlist making. Just turn it on and, if like me you are too impatient to learn the shortcut keys it is possible to use a mouse and mix away to your little heart's content. I have used it for 4 hours straight on a new macbook with 2gig of RAM and it hasn't dropped out at all.
So after that glowing review, can it be improved? Well, yes I think it would be useful to have a mid range adjust on the channel mixer. It would be good to be able to cut out channels 3 and 4 from view if they are not being used and put the crossfader between the 2 active channels to save space on the screen. It would be good to be able to enlarge the screen so that the pitch control is larger and more exact control could be gained.
However, if you are like i was a week ago, humming and harring about whether or not it will actually do what it's meant to do, the basic answer is yes, it works. Go buy it and get all you DJ equipment into a small shoulder record bag!