Upgrading... Don't know what to get.. DJs thoughts/opinions?

I'm not a dj. but.. you'll probably want screen resolution, and plenty of storage.

2.8 late2008 is still a hell of a machine, you will be downgrading if you get the 13" mbp or the air. An i5 will be faster than your current machine, but probably not by a great deal. You will have more battery life, but you will lose expresscard slow which is handy if you want to move 26,000 songs in a hurry.

I would max the ram, and maybe upgrade the hard drive from your (if you're still running on stock specs) and keep it until the 15" mbp gets a really significant update.

Unless like you said, you're mbp is on it's last legs. You probably didn't mention this to your buyer, did you?

Like the above poster said, Keep the machine. Upgrade the ram to 4GB or 8GB. Get A new, preferably 7200rpm HDD. And that computer could still last you 2 or 3 more years, if not longer.

For 1100 you could get a 2010 13 inch, upgrade to 1TB drive or 8GB RAM. If screen resolution is an issue, you could step up to the 15 inch but only at a much greater cost.

So after reading your post again, it might be better to just stick with your current machine and max out the storage/ram.

What sound card do you use?

I use Apogee duet (firewire), which excludes me from MacBook Air.
Already carry music on external anyway. Also firewire.

Might want a Mac with larger display if you like to see lots of songs on your screen.

the air will do anything the 13 pro can do minus the upgradability/battery life/firewire port

my friend is satisfied with the air since it runs all of his DJ software and it's thinner and lighter

traktor pro and ableton live 8, vdj, run very smoothly, like butter on my 13 pro, but I think you should just upgrade your 15" and it'll be fine for a while

or splurge and sell the 15", buy a new 15" high res anti glare