Try getting a USB soundcard, and just change the buffer until you get it right. Not much else you can do until there's an asio release for mac.

I am also having the exact same issue... I am fairly certain it was indeed an intel update that was the turning point. Does anyone with a mac know if installing osx leopard will solve this?

ok after searching on other message boards i found a solution to the problem. If you turn off Airport, Reason works just fine again! I struggled with this for months before figuring this out. I dunno if there are updates to correct this or not but turning off airport solves the problem for now.