The PC is like scuba-diving and mobile is like snorkeling, Rachel Hinman of Nokia told a group at the BAYCHI Interaction Design event this week. Luke Wroblewski's notes from her talk make fascinating reading for anyone interested in the mobile user experience.

Hinman talked about what she considers the most important attributes of great mobile experiences: They are uniquely mobile, they are sympathetic to context, and they speak their power.

To design experiences that are uniquely mobile means realizing what mobile does well -- it's small, always with you and good for timely information -- and use the constraints of the medium to help you focus.

To be effective in the mobile context, Hinman recommends designing for partial attention and interruption because mobile users need to be aware of what's going on around them. She suggests that the mobile experience is like snorkeling, and the PC experience is more like scuba diving.

In saying that mobile apps and sites must "speak their power," Hinman means that the interface must make its function obvious, like a light switch. She recommends ruthless editing: Focus on the main three to five things users want to do and cut out the rest.

That's the short version. Now go read the whole thing. It'll give you a lot to ponder.