I personally feel that an arcade machine is a piece of furniture where weight dosen't really apply, it's moved only once-in-a-blue-moon.
It's meant for semi-permanant installation.
I can't say this is necessarily true. I've had to move Supercade way more often then I ever thought I would, and I am very greatful that is doesn't weigh more than it does (it was built out of plywood). When we moved it into the current house, we had to go down three stairs, then back up three stairs, then through an extremely tight doorway. It took four of us to do it, and we about killed ourselves in the process.
Granted, it would have helped if I had taken the monitor out, and the next time I move, I assure you that's what I will do. But even without changing houses, my cabinet has been moved to three different locations in my living room, from the living room to the dining room, I've had to pull it out to replace the monitor once, and I have to pull it out frequently to work on the computer. How often do you have to change a whining fan in a dresser? Or troubleshoot why you aren't getting any video to a desk?
I'm not saying that MDF weighs too much to work with it, just that it is a tough call. Plywood only requires a small amount of extra effort, and weighs half as much. Of course you pay more for plywood, but if you've got the money and you're willing to put in a little extra effort, why not do it right?
I don't hate MDF. I've built two cabinets out of MDF. I only chose plywood for Supercade because I knew it was going to be huge, and every little bit of weight I could take off of it was a good thing. I am doing a classic restoration right now, and I am using MDF to replace broken pieces. I will probably use MDF for other cabinets in the future. But sometimes plywood is a better solution.
-Jeff "etumor"