Just ran my first pair of throttled builds. These two jobs were the only things happening in a 4-executor install.

So while one was running the other sat in the queue "Waiting for executor." Since there were three free, it looked off-hand like something was broken.

Please augment the queue mouseover to say something like:
"Waiting for build of [other project] to finish."
or more generically
"Build throttled. Waiting for blocking build completion."