Most of my professional growth is due to communities, they are the primary place where people share knowledge and where you can truly have a good exchange of ideas, knowledge and projects. The concept of community is the grounding fondation for Agile Culture, especially because they are not ruled by traditional processes. A community is more an ecosystem where ideas and people can grow togheter.
After joining UgiDotNet I toom part in the creation of another UserGroup called DotNetMarche, basically it is a smaller version of UGIdotNET but with a bound to the region of Italy I live in, called Marche. It gaves me the possibility to know a bunch of exceptional people and the ability to actively start contributing to a community, both as a speaker and as an organizer of Events.
I was involved also in an Italian community dedicated to Software Architecture called GUISA, but for a lot of reasons we were not able to make it grow a lot, so it is actually quite dormient.