[Al Skierkiewicz]

Building on Tristan's post, the single greatest improvement, from a safety standpoint, is having sufficient lighting to work with tools in your pit. When you cover the pit, it makes it difficult for your team to work. While I have seen teams mount lighting on the structure, I must remind everyone, that there is ultimately the chance for a shock hazard. I have seen some teams that were asked to remove lighting by UL Safety people as being unsafe. While on the subject, many of these coverings do not provide sufficient headroom. Teams that have used fold-up tents have used everything from soup cans to custom built extensions to get them high enough to clear inspector's heads and the robot on a work surface.
Of all the team pit designs, perhaps the one I like best belong to Apple Corps and Truck Town. They have lot's of storage, seem to be easy to move and have an open top.