Well, I was trying to stay away from here because it sucks time from sleep.. and then I see a post like this one :). I was in the exact same boat you were in; I had a good chance at a high paying startup in second year (I work for one now, and I'm done). I finished my Electrical Engineering degree, and it was one of the hardest things I've done - and probably, in the long run, one of the most worthwhile. Here's some reasons that made up my mind, some from me, some from friends and family.
First off: Because you started university, you're in a slightly different position than someone who never went. Maybe this doesn't matter, but not finishing will mean getting to explain why you didn't finish in many or all of your future job interviews. Not a pleasant thought.
University isn't about learning so much as it is about proving you can start something that's hard, multi-year, and requires massive sacrifice - and you can finish it. That's why I stayed - I had something to prove. It's also (one of) the reasons employers like college grads.
Second: Credibility. Not to diss smokedot.. But it's easier preaching legalization if you have a university degree, if for no other reason than you can play by the rules long enough to get somewhere. If you ever get arrested, that university degree might keep you out of FPMITAP (See office space :). I'm Canadian, and US drug laws scare the $hit out of me.
Third: Computers come, computers go. A university degree will never be taken from you, no matter what happens to the economy, linux, microsoft, whatever. It differientates you from the masses, and if you want to get somewhere in a corporation or large company, it's a prerequisite. I didn't learn squat about code in school. Or mpeg, or anything else I do to pay the rent. But my iron ring says that I can solve problems, even if I haven't been trained. I did learn about a lot of things I might not have touched - like advanced math, multivariable calculus, and OS theory - some of which has been most useful.
Fourth: Well, no other reason. See it out and you'll be happy in the long run, macaroni sucks in the short term though :).
The only exception to this if it's a once-in-a-lifetime opportunity a la Microsoft. You'll have to call that. If it isn't.. the jobs will be there when you're done.
Hope that helps.