@s3rius : Us mac users have not yet been graced with the map editor : ) Only PC beta users were able to use it as far as I'm aware.
I would still like someone with some know to answer the original question of like 4 of us above. This app opens the YABOT custom maps just fine, yet seems unable to open a custom map from anywhere else. It shows the loading screen, but then errors out to a "Unable to Load Map" notice, then redirects to the login page.
I have the exact same problem and question as dukaluke. The only map I've been able to play with using this utility is the YABOT build order testers. I've tried to load a few maps, including chupung ryeong and a UMS map, the hungry baneling, along with a handful of other customs. All start to load, but when the bar finishes I get the "Unable to load map" error as well.