It has to be very much off before anyone can hear or see it is.
Tor

I find myself using pretty large offsets to get just the right feel for particular subject matter. I might start with the fades lined up but rarely leave them that way.

The question was not really one of accuracy but to make the operation faster (i have a lot of cut to manage and a straight fade would have been ok to start with.

This feature is probably about the only one i miss from Premiere btw...

well you COULD do a copy then past event attributes I believe will work
but that will paste all event attributes
you could set a script to do this.

Are you looking to fade in AND fade out
or just looking to fade like 300 photos at the end of a movie
for example if you are doing a "photo mntage" and fading a lot of photos one into the other you could change the settings
- options - preferences - editing (tab)
make sure the check box for auto overlap is checked
then select the amount of time to over lap / fade
voila you're done

Not sure if this would work for you, but there is a setting in Preferences that adjusts the automatic fade of audio events. The purpose is to avoid unwanted noise that results from cutting im midwaves etc. I guess you could set this amount high enough to provide a real fade (have not tested how far it will go). That would give you a fade in all audio cuts which you could approximate with your video fades afterwards.

If this is a major concern form you, you could create an empty event (Full transparency video and silence - synced and grouped) and use it to overlap the real events of your project. That would give you equal fades for video and audio.
Tor

I think this can be scripted.