For users experiencing this issue, you can narrow down the cause of the slow shut down using a simple Terminal command. Open Terminal and enter:
pmset -g logThe "Signature" with the longest "Response Time" (in ms) should be the first program to look at. Users should be sure they have updated all their third party applications and plug-ins, especially after updating to Snow Leopard 10.6.2, to ensure the best compatibility.
Several users report that the GoogleTalk plug-in for Firefox or Safari was their culprit for the longest response time when attempting to put their Mac to sleep. Several other users also found that they had an outstanding print job in their printer queue.