Actually, I'm going to report *some* success with the ultrasonic repellers for mice at least. Our last house was a cottage on the edge of a wood, and every autumn after the first frosts, the wood mice would move into the loft. We never had them in the house itself, but still couldn't really live with them up there due to the electric cables and fire risk etc.
Anyhow, whilst we did still catch (deaf?) mice in the traps after we installed the ultrasonics, the numbers were definitely down (say from one or two a day in September to one or two a week after installation), so they did have a limited effect over a small and well defined area. Not sure about the rats though, or how it would work outdoors.