My experiences match Swanhunter's. Normally things seem to work nicely at DFW, especially if you're off in J/F. However, with delays from BA or other airlines, if you run in to the LH or Mexicana flight at the same time it can be a pain and a bit of a zoo. But then so can SFO with delays. And LAX more often than not is a right old hole. Avoid LAX like the plague I say.

The 'new' DFW Terminal D immigration hall is a lot nicer though and does seem to be generally quite well staffed. My sympathies on the extra screening - though that can also happen at any entry point

I hope I haven't jinxed myself for my next arrival in a couple of weeks!