@gailcalled, I suggest taking some items into consideration. The purpose of the weekly backup is to make a complete snapshot of the system in case of catastrophe.
For certain heavy-duty apps with an internal database behind the scenes, if you’re in there working while the weekly snapshot is going on, then you might find certain items are out-of-sync where the backed-up copy of the database says one thing, but certain other elements reflect a newer status.
So, what would those heavy-duty apps be? I’m thinking Apple Mail (or Thunderbird), iTunes (just don’t import), iPhoto, and similar items.
It would be totally fine for you to surf the web, visit Fluther, use web-based email (like gmail), etc. If you so choose, you can also elect to edit documents and the like in Microsoft Office or Apple iWork as those are usually discrete items not tied to a set of hidden metadata.
Just my $0.02.