Not the delivery service (though I love them too), but Uninterruptible Power Supplies.   I just had a circuit breaker blow three times (until I figured out what was causing the problem!), but nothing bad happened to my systems.   Considering how much I always have running, just having the power disappear is a Very Bad Thing(TM).   I recently bought a ~$30 UPS power supply which is more of a fat circuit breaker strip.   It's not all that powerful, but it's more than sufficient to keep me going for five minutes while I reset a circuit breaker.   What a great investment!   Don't wait until it's too late to pick up one of these...