[Matt Stutter]

I know the very problem you've got, and it's PITA. But, if you open up your transport window, then Choose the option to Display MIDI Controls for the Transport Window you'll see a little "2 Bar" box, this'll be white and this indicates a wonderful 4 second pause before recording starts. (or two bars)

Apparently it gets turned on after trashing prefs or something.. Lovely default, not!!

But yeah - if not that try all the other things mentioned here, although they point to larger problems and "system wide" issues rather than session specific anomolies.

Regards,
matt.