The update fixed a flaw where subscribing to a maliciously crafted photocast could allow a remote attacker to run arbitrary code on your computer. It also improved overall stability, and fixed several other minor issues.
iPhoto is part of the iLife suite which is priced at US$79. The iPhoto 7.1.2 update is free for all iLife i08 users and is available via Appleis Software Update application or as a downloadable installer from the Apple Support Web site.