When you check the DOF box the entire scene goes fuzzy. It's a bit 'hit & miss' to pick the point on which you want the camera to focus.
Could we have a small clear circle centered on the cursor which shows the clear scene through the 'fuzziness' and which follows the cursor until you have picked the focus point.
Sounds like a good idea but I haven't had too much trouble picking the spot myself.
Click roughly where you want it, wait a second for that to res up and then click exactly where you want it. I appreciate it would be much harder if the target is quite small compared to the background though.