I have a faucet that does the same thing.
The other day I bought some LED light bulbs to replace the incandescents in a light fixture. The light was on most of the day and evening until I went to bed. When I got up this morning, the bulbs were glowing faintly – one brighter than the other four. I removed one of the bulbs and it and the others continued to glow. It doesn’t look like phosphorescence; they seem to be on, but at low power.
It’s not a problem in this particular application, but it would be in others. When I turn a light off, it should go dark. If they can’t make that happen, the manufacturer should market it as a feature – “New, Afterglow® technology!” – and charge a dollar more.
UPDATE: Less than three months later, 2 of the 6 that I bought have stopped working. Whether because they’re junk or because my old house’s wiring is bad I don’t know. But it’s something I’ll have to take into account. They also had a depressing blue tinge, and were far dimmer than the package claimed – almost unusable. I’ve put the rest in some little-used fixtures. I’m going back to incandescents for now.
UPDATE 2: This short post on LED lighting may be of interest.
UPDATE 3, 12 October 2010: Dave Farquhar “got an LED bulb, and it is fabulous”. I’ll have to give them another try.