
Sync is NOT painful in the DSLR world. Back in the film days, it was painful. You had to have an assistant go stand in front of the talent and whack the clapboard a couple of inches in front of his nose because you needed the visual slate as well as the sound. The DSLR has a built-in mic, so it captures sound too and you have that as a reference.
What I do is simply whack the slate out to the side, don't even bother with a visual slate. That gives me a spike on the camera audio as well as the recorder's audio. It will be louder on the camera since I'm standing there, but it's not a problem.
I drop my video and camera audio clip in the timeline. Find the clap, mark an in point one frame before. Then I drop the recorder audio into the player window, find the clap and put an in point one frame before. Edit it into an audio track below the camera track, and about 95% of the time I'm right on. Sometimes I may have to slip it one frame left or right if I've mis-marked the in point.
It probably takes me a minute or less to sync a clip.
Be sure to add a verbal slate too, to identify the subject and take for the recorder, otherwise you might have trouble matching the right sound to the video.
One other thing I do--FCP will show you with red numbers if you move something out of sync when editing. But the audio from the recorder has no relation to the video clip. So what I do is unlink the camera's audio track and link it with the recorder's track after they're in sync. That way if I slip sync when editing, I'll get the red numbers. Obviously, take the camera track level down to zero after the tracks are synched.