I'm using Leopard and a new Mac with the function keys mapped to hardware functions. So, in EF, I know I have to press fn before F1 to add a item.
Adding things from Mail takes two or three presses. Adding web pages from Firefox takes up to 10 tries.
I've experimented with long presses, short presses, long press on fn before pressing F1, etc. No clear favorite. I just repeat till I hear the sound and see the action in the Activity Viewer. I've also checked that nothing else has F1 assigned to it.
Using Drop Pad works on the first try, but it's easier to press a key. And, since I'm using Spaces, Drop Pad is not always visible.
This happens with EF 1.2.7b3, but was the same with EF 1.2.6.
EF 1.2.6 with Tiger on an old G4 responds every time to one simple press on F1, so it seems to be either the new Apple keyboard model or Leopard.