The most challenging thing for design at Facebook, Aronowitz said, is the debate on speed versus quality.

FORBES: Design For Facebook, Mint, Posterous Not Just Pretty Pixels

These days the best designers are not just doing one small part of the design process, Aronowitz said.

FORBES: Design For Facebook, Mint, Posterous Not Just Pretty Pixels

One tweak to Facebook photos increased the number of tags added to Facebook photos by 2.5 million per day, Aronowitz said.

FORBES: Design For Facebook, Mint, Posterous Not Just Pretty Pixels