I recently noticed a message telling me to wait for 5 seconds between successive searches. Has it always been like this? I don't remember seeing this before. Or is this a new feature added to handle server traffic?
Yep, it has been (although it may have been 10 or 30 seconds a long time ago).
Especially annoying if your search yields nothing and you want to remove one of the search terms, or if you made a typo :-)