There was a recent post on HN about a startup in Seattle spending loads of time to build door desks, an apparent attempt to emulate Amazon. Perhaps purchasing ergonomic desks for a reasonable price and no time sink would be a better strategy than these clunkers.
My variant is to lay two 2x4s across either two filing cabinets or sawhorses, then put two 2'x4' sheets of 5/8" or 3/4" MDF on top of the studs. Cheap[1], toolless[2], and portable[2]. My current variant is a little more elaborate, since I wanted a corner desk, but fundamentally the same architecture.
[1] The sawhorse version costs less than $50 [2] Nothing is attached
1. The metal reinforcement underneath the tabletop, around the perimeter, would interfere if you wanted to install a keyboard tray.
2. The collapsible diagonal metal struts that reinforce the legs reduce the usable space underneath the table somewhat. You may not be able to fit a filing cabinet (or small rack, or tower PC with hard drives on top, etc) under a folding desk near either end, because of the struts.
I suppose there is a positive in the pride of workmanship and if someone is handy and feels like doing this - have at it. The monetary savings don't seem worthwhile. If they exist, they are purely symbolic - at least for a company that can afford to pay rent.
http://www.officemax.com/office-furniture/tables/folding-tab...
http://www.staples.com/Staples-8-Folding-Melamine-Banquet-Ta...