The big deal with MDF isn't just weight, it is durability.
Furniture made out of MDF and particle board falls apart over time. You are lucky if that stuff lasts 10 years. Plywood furniture lasts forever.
Paige,
I agree that in some ways plywood is more durable than MDF (e.g., it should last longer and it isn't as susceptible to water damage). But MDF doesn't chip like plywood, especially when cutting (a big deal if you are building a cabinet yourself). Particle board is another story, I wouldn't use that stuff to build anything of value.
Longevity is moot, I think that most of these home built cabinets aren't expected to last 10 or 20 years, like some classic games ended up lasting. Most of these mame cabs will be burnt or cut up down the road. The electronics will go bad or be moved into something else LONG before the cabinet falls apart from age. Also, these games typically are in basements, not barns or outside locations like beach boardwalks, etc. And even a lot of those games managed to stay together over the years.
There is also a variety of quality to materials. It's true that most cheap furniture doesn't last but it is usually really cheap MDF or particle board. I can say that the MDF I bought for < $20/sheet is going to hold up a heck of a lot better than most of the cheap furniture I have around.
I typically go for the "you get what you pay for, it's usually worth it to get the higher quality stuff" etc. mindset, especially with bigger purchases. But unless a person is building a cabinet with a stained wood finish, I just don't think it's worth $150 for plywood for a cab vs. $50 for MDF, when MDF has almost all of the best qualities of the common cabinet materials.
Though, this is just a matter of opinion, we can respectfully disagree. Every time the material question is asked, most suggest MDF, and there are always a few that suggest plywood or particle board.
Wade