We have identified the issue with the Mac edition crashing -- it was due to the new card pricing code we put it to handle the larger number of stores that are coming online. Basically, if your Mac loses it's Internet connection, the new card pricing code will cause the app to crash (we had inadvertently set the retry timer to 0).
We have already submitted a patch to Apple to fix this bug. We apologize for the issue, and hope the patch gets released soon. In the meanwhile, to avoid any issues, you might want to make sure your Internet connection is up while using the Mac edition.