I use wunderground whenever i want to know the weather. I find it does better than other websites like weather channel, etc, mostly because it can forecast to individual neighborhoods, not just entire cities, because they encourage people to connect personal weather stations to wunderground to give them more data. Now that I have my bloomsky hooked up to it, I can use all of wundergrounds nice algorithms to get a forecast for my house. They also have one of the best radar maps and APIs around.
You can make a weather tile in smart things with this to pull the weather underground data into smartthings. You dont need your own PWS to do this, but if you have a bloomsky, thats just another way to pull in the data. Then you can use the outdoor data to trigger events, like turning up the heat if its super cold out, or turning on a fan when its hot and no one is home, etc.