I use one for a hallway light in the house. It's on from about 1/2 hour after dusk to 11:30. Mine has a few LR44 batteries in it. I did have to replace mine once for whatever reason.
It does have a exterior button that can be depressed to turn the light on when it's off, but it's too difficult to reach being behind a cabinet. At night, there are usualy 3 light on in the house:
1. A 7W incandescent night light in the kitchen it's on most of the time)
The kitchen has a ceiling light, a light over the sink, an over the table lamp (2 of the 4 lamps are mini CFL's), a table lamp, a "hall lamp", an under the sink lamp and the refrigerator lamp. The fridge lamp is a LED based. The socket was close to unobtainium, so when it was replaced, I replaced the lamp with a LED version. The lamp itself was hard to find and had to be modified. The center connection had to have increased height.
2. the astronomic timer (CFL)
3. A night light with an LDR in the bathroom (LED)
The two reading lamps in the living room are 3-way LEDs.
My elderly mom (wheelchair bound) has a UPS on a high intensity lamp in her room. The UPS also runs the answering machine and cordless phone base station (4 phones) and is primary backup for the medical alarm.