I ask because upon initial install, this program (newest version) is PAINFULLY slow, and slowing down my system extremely, toward the end of the 6k block mark. I'm wondering if you force quit the application before it is completed, it will start all over again, or do something else.
The QT client at least should gracefully resume from where it left off.
I have done this many times with no issue (running a reasonably recent copy of the client in Windows 7).
I'm not sure whether the MultiBit or Armory clients work the same way though; can anyone vouch for them?
The client will continue downloading blocks from the last successfully downloaded block.
As far as database integrity when this happens -- BDB has crash recovery that generally works without any user intervention but doesn't accommodate a number of scenarios, so maintaining backups are highly recommended.
Here's more about BDB's recovery method: