According to a Grid Status Update today, there are "Issues Opening the Second Life Viewer in MacOSX" (Web). The post points to a possible fix at a third party site called OS X Daily (Web). I've had no troubles with the official Second Life viewer, despite a number of reports such as this JIRA (Web). I'm a member of the Macintosh Users group in SL and can highly recommend that all Apple users join. Good luck, fellow Apple Geeks!