I have a mortal (yes, irrational) fear of spiders. I live in a flat and was getting about 6-10 a week that were about 3 inches in length. Getting desperate, since I can't go near them to dispose of them, I bought one of these. It says to give it a couple of days to see a difference, so seeing 2 the night I plugged it in was okay. That was the last 2 live ones I've seen and I've had the unit for 4 weeks now. It's plugged in in my hallway which is more or less the centre of my flat and appears to be keeping the place spider free.
For those who've said the unit is noisy, perhaps their unit is faulty as mine is silent and I have it on the high pitch setting.
I live in fear of powercuts now.... :)