This SXSW presentation covers: the elusive ingredients of "tapworthy" apps; why building iPhone apps is like designing a physical gadget; usability gotchas on handheld devices; and how the best iPhone designers turn constraints — limited screen space and fleeting user attention — into advantages for their apps. Along the way, Josh shares behind-the-scenes glimpses into the design process of popular apps including Facebook, Twitterrific, USA Today, Things, and others. The presentation is by designer, developer, and author Josh Clark, previewing ideas from his upcoming book, "Tap Happy: Designing Great iPhone Apps" from O'Reilly Media.