Photoshop panels are always great ideas. We of Creation Station have run them at various cons. Marie Tary, a professional webcomic artist and graphic designer, has run them for us in our rooms at previous Sakuracons and Anime Evolutions, and JeniOctavia ran a How-to panel on Photoshop Layer Masks for Creation Station at KC '08. I would be delighted to hook you up with them either to help you with ideas (for example, they could tell you what audience members were most interested in), or potentially, to help you present, if that's something you'd want.
Please PM me and/or join:
the_creation_station@yahoogroups.com
And best of luck with your panel!