We're on city power (LA Dept of Water and Power), and we seldom have full outages. We do have a lot of power dips, but I think those are related to overtaxed wiring in our house, not the power supplier. According to the battery backup software on my computer, my system switches to the battery 5 to 10 times daily, but these voltage aberrations are not enough to reset the clocks and VCRs in the house. I have the sensitivity on the backup battery set pretty high, so it kicks in at the first sign of a non-optimum voltage.
Frank, if you want, I can edit the poll to add a few (less frequent) choices.
[Edited to add]
Now that I'm home, I just checked my UPS logs and I was wrong about the number of events it records. In the last month I've only had 13, with the system on battery a total of 1 minute and 5 seconds. The previous 5 to 10 times daily was what I was seeing when we first moved into the house, so apparently something has changed for the better in the last three years. Also, the log is showing all 13 of the events were blackouts, with zero undervoltage or overvoltage events.