This would have been great to have when the only Multi-Table lookups were the Customer fields, but now that custom Multi-Table lookups are being added, this will become all the more useful.

I'd like an "is" condition added to the platform and the various query editors... Advanced Find, Workflow Check Conditions, etc.

This way you can build workflows like:
If Customer is Account, then do something.
Else if Customer is Contact, then do something else.