1: Wildstang had a video of their 2008 crab with a dummy trailer up, but it got taken down for some reason. It was unclear, however, whether they were "crabbing" in the video. It seemed to handle relatively well, but not particularly better than some of the better looking 4wd robots posted so far. Perhaps someone from wildstang can give us more information about this test.
2. It depends on your resouces. However, crab takes a LOT of work, and nearly all teams that use crab prototype their crab design in the offseason. I cannot say that I reccomend it, if no serious thought to your crab design has been given until now.
3. Haven't seen one either. I would recommend searching the images on chiefdelphi for crab/swerve drives, and contacting the designers for more information.
Some teams to check out for crab designs:
71
111
118
1625
973
Miscellaneous CADs by CraigHickman
4: All custom machined. Precision tools are usually required to make these parts, which if you don't have access to, would throw a wrench into plans for a crab.
Finally, there have been several videos of skid steer robots posted, many of which seem to be moving quite successfully. 1629's "wide orientation" video posted today particularly stands out.
http://www.chiefdelphi.com/forums/sh...threadid=71861
The bottom line is, unless you are sure you can design and build a successful crab in the next few weeks, I would look more into variations of a skid steer.