O'Reilly Open Source Convention ("OSCON")
As its name implies, an open source convention sponsored by O'Reilly (the publisher of many useful technical reference manuals and how-to books). I attended an OSCON about ten years ago, chairing a birds of a feather session about FreeDOS. Topics at OSCON span a broad range, and I think a presentation on open source usability would be well attended.
An open source software (and science fiction) convention held annually. I was a Nifty Guest some years back, speaking about FreeDOS, Linux, open source in the enterprise, and building open source communities. The date and location for Penguicon 2013 haven't been set yet, but based on last year's schedule I would expect it in late April or early May.