Sometimes I do dumb things. One example is that I often forget to stop running an executable before attempting to rebuild it. The AppBuilder eventually fails because the file is locked--it can't delete & recreate the *.exe file if it is actively running--but sometimes it takes several minutes before the AppBuilder gets around to checking that. It would be nice if it did the file permissions check earlier in the process, so my foolishness doesn't slow me down excessively.
Also, since the "cancel" button for builds doesn't actually do anything, even if I notice it immediately, I'm still stuck twiddling my thumbs for a few minutes until the AppBuilder *realizes* it can't complete the process....
