I had a buddy with a D600 (hall mate in the dorm 3 years ago). In fact he was telling me how much he liked it the first couple months he had it. At that time I was debating between the D600 and the I5150(amoung other laptops), decided to go for the 5150 because it seemed like a better value. I regret it. Latitude's are supposed to be more rigid for business usage, I couldn't tell you long term though(lost contact with the guy). As for my Inspiron 5150, I loved it the first couple months as well, until the motherboard went out twice!(bad case design, a piece of plastic on the bottom mashes the soildering and connections, and the case flexes).
I'm willing to forgive dell, mainly because they have such good customer support, I have a 4 year complete warranty so they do fix it... but I had to ask for an extension on one of my papers because of it, and I also got screwed on a roadtrip when it went out on me. So what am I trying to get to? I can't conclude personally whether or not the D600 is reliable and tough(I can conclude it for the 5150however), but if you do bite on Dell's attractive deal, CERTAINLY GET THE EXTENDED WARRANTY, along with the complete care, it gives more than a piece of mind if anything does go wrong.