"Does anyone else have one of those things you can use to trace which breakers are running which outlets? "
Yes. It has come in VERY handy over the years.
"An electrician buddy said my house was good to go, but there are some odd groupings - for instance, the bathroom outlet and the outlet at the back of the house are on the same circuit."
Actually, not uncommon at all.
My house was built in the mid 1970s, when GFCIs were expensive as hell. Bathrooms and outdoor circuits were required to be on them, but kitchen circuits were not at that time and they would often chain the outdoor and bathroom receptacles onto a single GFCI.
About 15 years ago I recounted here how my bathroom receptacles were working intermittently. I couldn't figure it out until I finally realized that the GFCI in the basement next to the power panel controlled the patio outlet, the half bath outlet on the first floor, and the outlets in both bathrooms on the second floor.
I then discovered that the patio outlet, which was back stab wired, had a failed clamping spring in the one backstab, so it was only intermittently making contact. I replaced that outlet, wiring it properly, and rewired the bathroom outlets properly, as well.
No power problems since.
