My Mom has the original builder's kitchen in her condo and it's a minimum of 20 years old. Melamine over 5\8 (might even be 1\2 inch) particleboard. Hinges are going but they have not come loose from the cabinets or doors (which are also melamine - maybe over MDF but I doubt it). I've attached a link to the ANSI ratings for particleboard so you can look at the properties of the various types. Usually Commercial or Industrial grade is used in quality cabinet construction (either M-S or M-2). Ask the cabinet maker or manufacturer what they are using. Of course the method of assembly is as important, staples, plastic corners, full valances, tongue and groove, doweled and glued, full backs or thinner hardbacks with hanging rails, cross valance between gables behind the toe kick, just legs, wood face frames - some of these are preferable to others. Are your edges at least colour matched to the door? I can't say for veneers but what is the veneer being mounted on? 3\4 MDF would be my guess if they are solid. This good a number of high end companies now offer their painted finishes on solid MDF doors - no cracking like on 5 piece mortise and tenon doors. That's what I picked up I'm sure some of the KD's no more for sure.

Here is a link that might be useful: ANSI guidelines for particleboard standards

I've had both and have no complaints about either. I really like the easy-clean of melamine, but the plywood is OK on that score, too, if it has a good finish. I just worry less when I think of the possibility of putting away slightly wet dishes on a melamine surface, and they're nice and bright inside. My dh makes our cabinets, so prefers the plywood, because he loves wood, for one thing, but also because it's lighter weight, so easier to cut and the finished cabs are easier to move and hang. That's why he 'won' and we have plywood in our new house.

I'm fine with the Melamine: it seems to make the interiors brighter, it's easy to clean, almost seems to repel dirt.

I don't have a thing against ply, and used it in all the baths. But in the kitchen, I think there are better ways to spend the budget.

Melamine will not hold screws or glue as well as plywood. It also does not like water. I have done insurance work over the years where the dishwasher/ice maker/sinks, have leaked. The bottoms of the cabinets (under the sink) and the sides near the floor become sponges, soaking up water. If you don't catch the leak right away you have a big problem. Many times the only fix was ripping out the whole cabinet and remaking it. Also the shelves will not hold as much weight either. If the drawers are made of Melamine stay far far away. So I guess you can say I favor plywood constuction.

I am also in support of plywood. Melamine is a nice hard surface until something penetrates the hard layer outside. The inner core swells up so easily. I prefer plywood construction for to many reasons to list here. If I were doing my cabinets in my house 3/4" ply construction with face frame and dado construction is the only way for me. Also solid wood dovetail drawers, other construction just does not hold up.

bigfatcat, thanks for posting this question. I have not been able to get a straight answer out of anyone I have asked about this same question. I am trying to decide between two different places and I think I am going with the place that offers all plywood w/o killing me on the price.

No question that if you constructed two cabinets in the identical manner the plywood cabinet would be stronger. A badly made cabinet out of plywood isn't going to last longer than a well made one out of a decent grade of particle board. Simply put plywood does not make cabinets good and melamine over particleboard does not make them bad. More than one poster here, myslf included, has talked about the too long staying power of their horrible particle board builders kitchens. Wood dovetail drawers are great but not in all our budgets, a good metabox drawer will perform well for a long time. Stapled melamine with a 1\4 inch hard board base is sign to turn and run. Quality construction is as much about how things are constructed as it is the materials they are constructed from - it's relational.