Thought I'd bump this thread, mainly because I have two of them (Andy at Stompblox was generous enough to send them to me for review).
First off, they're not big at all; about 9" x 12" by themselves. However, they are SOLID. They look to be bent metal frames, and are very sturdy and heavy. They lock together pretty easily, and the thumb screws that keep them together are attached, so you don't have any small pieces that you could lose. When the two are attached together, there's no flimsiness. They are locked together. Given that with two, you can make either a 9" x 24" or a 18" x 12" board, I like the options. There are also feet on the back of each of the boards to allow you to have a bigger slant on the board than just the board itself (which has a slight slant).
They each come with a bag, that's a 12" x 12" square, roughly. The zipper on the bag is much like the zipper on a sleeping bag, meaning that if you have two Stompblox boards that you have screwed together regularly, you can zip the two bags together and make a larger bag to fit the board.
The underside of the board has plenty of areas for zip ties and cable management. I was even told that with the feet out (for a higher slant), you can easily put a Pedal Power II+ under it. There are plans to release a CAGE unit that will add another ~ 5" on the back (I'm assuming to make a 14" x 12" board) which will allow you to store up to the Voodoo Labs Mondo Power Supply.
MSRP for each board is $80, but they're figuring they will sell around MAP, which is going to be $60.
For myself, having one small board of my "essential" things (DI, compressor, EQ pre, delay, effects loop) and a second with extra pedals (distortion, envelope phaser, chorus, etc..) that I can attach quickly and hook up easily is a huge bonus.