My colleague has one at work. Our office is generally farily light but she does switch it on when the day is particularly grey. I'm not sure that she actually has SAD though. I've never known her to be properly diagnosed and if she did have SAD, I thoughht she'd use the box all winter to extend the day light hours? As it is she's quite intermittent with it.
Does seem to work for some people I know - but you may have to be prepared to 'just sit' in front of it for the relevant time - the light is so bright that you won't necessarily be able to read or do much else whilst using the lamp.
And make sure you buy a real 'certificated' model - not just a 'bright reading light'. Read the reviews on Amazon to get some more ideas abbout which ones work and what the good/bad points are.
Have just heard of it recently and its just surprising the people who would feel down at this time of the year .does it work just when being use or does it provide a lasting remedy