This site, along with the others I maintain personally, run DotNetNuke. For those old enough to remember, DNN is based on IBuySpy, I actually work with one of the folks responsible for the original IBuySpy code and site.

Recently, DNN announced a security issue and here, just a couple of weeks later, they had an upgrade ready to go.

I personally like DNN. The modules and skins are easy to implement. I was able to take a couple of pieces of code I needed to handle WebQuotes and the like with very little work. It may not work for everyone and I still have some issues with my code I need to work through but it demonstrates that frameworks and open-source can work, even in the Microsoft World.