Although Boost was begun by members of the C++ Standards Committee Library Working Group, participation has expanded to include thousands of programmers from the C++ community at large.
If you are interested in participating in Boost, please join our main developers mailing list. Discussions are highly technical, and list members are encouraged to participate in formal reviews of proposed libraries. There is also a users mailing list, and several project specific lists.
If you are looking for more lively interaction with the Boost community there are also some internet relay chat channels that users and developers like to hang out in.
Below is a community maintained calendar of Boost related events. Mostly this includes development of the release. Note that schedules slip and this might not be up to date.