I have the "Open Last Used Brain at Startup" checked in the Advanced options. This works great, but I noticed something that I thought I would share in case it should be corrected.
If you close the current brain and exit with no brain open, the next time you start PB, it opens with the last brain you used.
Now I understand that is exactly what the option says it would do, but I thought it would make sense that PB would start with no brain if it was closed with no brain open.
Just my two cents...