Practicality of solar in northern latitudes

I have heard a lot of arguments about how the further north one gets the less practical solar energy becomes. Bob, seeing that you are from Wisconsin, could you give us your take on that?
Thanks!

Solar water heaters work great in northern climates. A properly designed solar water heating system can last a long time with no problems and provide lots of hot water. It is certainly the case that during the cloudy winter you will not get as much hot water as you will during the summer, but the investment is well worth it. People in Alaska, Canada, Norway, Sweden, Finland, and all very Northern countries are typical solar water heater users.

Bob