More expensive than showerboard, but it's glass -- so it erases forever and looks great. The % savings compared with commercial glass whiteboards is astronomical.
If anyone considers this, please us tempered glass. This says 'tabletop' so I assume it is. It's not a whole lot more expensive but it's much less deadly.
Thanks for the awesome link, I'm surprised I missed this Ikeahacker post. I might have to bring a dry erase marker along on a future trip there. I'm definitely going to do this for a future home office upgrade. Now I just need plan out some kind of dead simple rig for taking photographs of the whiteboard that would automatically sync with either Dropbox or Evernote. This might be a good use for one of my old android phones.
We did exactly this for a coworking space in town.
I suggest using a full-length bracket all along the top and bottom and siliconing the tabletop into place, and then putting little brackets on the sides.
You don't need the chipboard backer if you just screw it to the walls at each stud (every 16" here in the US). Have sure you do both the top and bottom though, otherwise humidity may warp the board away from the wall (I'm looking at my first attempt as I write this which has warped, my second which I screwed on both top and bottom has not)
Get a 4x8 sheet of shower board from Home Depot. It's basically just a thin piece of melamine, and should be like 8 bucks.
Get a 4x8 sheet of really low grade 3/8" or 1/2" cedar chipboard (like that used in flooring), again maybe 3-4 bucks.
Glue the former onto the latter with Liquid Nails, probably 2-3 bucks a tube.
Works great, erases, and when it finally gets too gross to use (in about a year), you replace it for another fifteen bucks.