They are excellent, I wouldn't be with out mine.
I run an automatic BMW, plus I drive to the alps once or twice each winter, and have done for many years.
I run these:
http://www.nokiantyres.com/tyre?id=2...kian%20WR%20A3
which are excellent and recommended.
I run them from mid Nov until end of March, or when it just gets about 7 degC after the cold season, so 4 months or just a bit more.
For me its a no brainer. total grip, breaking ability and traction in the snow and ice. Excellent through the cold wet, and winter months. Just so much better to drive the car with them on, and know that the family is safe and I won't get stuck. I also have snow chains, but haven't had to use them in this country with this car as yet, but they are in the boot. I've used them previously with other (company cars) when i've not had winter tyres though.
I bought a mint second hand set of 16" bmw rims and got the tyres in summer months (cheaper). I'll get 4 winters out of them, certainly 3 on the rears and more than 4 on the fronts, so that's extending the life of the summer tyres as well. I keep them at the back of the garage and swap them out myself.
I'll also recommend mytyres.co.uk, it's where I got mine, delivered direct from Germany.
Anyone who thinks they are "not worth it" is quite frankly a fool. If more/all people had them, this country wouldn't be in such a bloody mess in winter when it's icy and cold. We should have a euro style law where it is mandatory in the winter months.