Can anyone tell me if an anamorphic adapter completely disables the auto-focus function on mini-DV cams, or does it just make the auto-focus slow and tempermental?

Depending on light levels, contrast and other factors, the adapter my confuse the AF mechanism. This may result in slower times for the focus to lock on the subject or even inaccurate focus. To insure focus accuracy the camera operator may want to disable the AF mechanism.

Thanks, that's what I was wondering. I don't understand how people focus manually, since I don't know of any company that makes an LCD screen with a high enough resolution, even the expensive ones. I was hoping I could get away with flooding the subject with light and letting the autofocus lock on, then putting it in manual so it won't shift on me. Sounds like that would work.

When in doubt, test.

Use a reasonably large monitor attached to your camera for focusing if you don't have a high-res viewfinder.