The 2014 Linux Plumbers Conference (October 15-17, Düsseldorf, Germany) has sent out an advisory that the registration limit is about to be reached. "We are very rapidly approaching our attendance limit, this year faster than in any past editions of the conference. We expect that the conference general registration will be sold out soon, possibly even within a few days. If you have a vested interest in participating in the discussions, please register now, to guarantee that you will obtain a ticket for the conference."
Also, the conference is seeking submissions for Microconference discussion and BOF topics.