AppleInsider expects that Apple will update its complete laptop line (13" MacBook and 15/17" MacBook Pros) to Core 2 Duo "Merom" before the holiday shopping season starts in late November. According to the site, development has been completed and the launch is simply awaiting Apple's marketing team to "pull the trigger."
MacShrine and MacOSXRumors expect the MacBook Pro to be updated at Apple's September 25th event preceding Photokina. AppleInsider is unsure whether the updated MacBook will be unveiled at that event or be held off to ensure adequate supply of Intel's Core 2 Duo Merom chip.
Many users have pointed to extended ship dates and delays for MacBooks as evidence of an impending update. While possible, the shipping delays may simply be due to a demand backlog which was noted in Apple's Q3 2006 conference call in July. At the time Apple stated they expected to reach a supply/demand balance by the end of September (the end of Apple's current fiscal quarter).