I'd say I see about 75-80% of plays well enough to clearly know what foul/violation (if any) should be called.
For things which are clearly violations or fouls, I try to call 100% of them, but I'm probably at about 95% (Hey, we all miss some!).
On things that might be violations, I try not to call them. For "kinda-sorta" fouls, it really varies depending on the game and what kind of mood I'm in that night (
) - I probably call half of those (which half depends on which team bribed me better before the game!!)