@JohnAskew: Yes we're in the UK and this is the worst place I've know for power cuts; we're in a rural area with several farms and one huge aircraft factory.  Most of the outages are 'pre-planned' but we still get the occasional surprise (such as turning up to work two weeks ago to a dark, quiet office).

My boss owns two surprisingly small generators which we can use to power most of the office (servers and all) so when we get pre-warning we can still keep working.



EDIT: when I say 'frequent', I really mean 'two or three a year', just so you don't think it's constant -- just often enough that it's no longer such a surprise.