This may be old news to some, but I thought I'd share this for those who don't know. I just found out about the Okii USB Focus Pull about a week ago. It is an electronic focus puller for DSLRs. I got it for my 5D MKIII.
This thing is amazing!! You can program two different focus points and have the Okii rack from one to the other at any speed you would like. It isn't cheap, but if you are wanting to do some serious filmmaking then it could be a huge benefit. Check it out here:
FC1 USB Focus Controller
When I first started playing with it, I decided to do something more interesting than just a bunch of random test shots. So I made a little short. Check it out here if you would like: