We've got four UPSes in the house: one in the machine room, as mentioned; one 350 VA unit in the attic, to power a single Ethernet switch for the upstairs backbone; one 500 VA (I think) in the office, to power Paul's Linux box (and I need one for the Mac); and one 500 VA unit in the basement, to power the other backbone Ethernet switch, the DSL modem, the voice-over-IP telephone adapter, and the firewall.
Unfortunately, all of that was less useful, this time around, than I'd intended. We use two low-end PCs for the firewall, alternating between them as software upgrades and the like happen. One of them had failed while I was in LA last, and the other was brought into service. Only one problem: Neither of us thought to plug that box into the UPS. We had a running network that couldn't communicate with the outside world because the firewall was down. Grumble.