On today’s home page for MacFixIt there is a report that some OS X users have to authenticate to their Macs twice in succession in order to wake up their machines. This issue has been also documented on the Apple Discussion Board. I have experienced this problem with Leopard on numerous occasions. One suggested workaround is to change the account password in System Preferences, and then change it back to the original setting. I initiated the suggested procedure this morning and will test it out later in the day.