I turned off the screensaver password so I'd be better able to see what was happening with my rMBP when it woke. It's easy for me to check on Mail. If Power Nap is working the junk mail is filtered out by the rMBP when I check my email on the iPad.
Well, Power Nap WAS working until last night. As best I can tell, Mail and TM didn't run even once all night.
I know it was active because I was testing to see whether Power Nap was working with Find My iPhone from my iPad. The rMBP showed up after it went to sleep and again before I woke it up. Also the rMBP's casing was slightly warm...it's normally cold after a night's nap.
Console didn't reveal anything interesting that I could spot, except for two warnings about Mail...
8/4/12 12:34:32.941 AM SyncServer[1378]: [0x7fbfd040bd60] |DataManager|Warning| Client com.apple.Mail sync alert tool path /System/Library/Frameworks/Message.framework/Resources/MailSync does not exist.
8/4/12 4:05:50.917 AM SyncServer[1561]: [0x7fc933c0bd60] |DataManager|Warning| Client com.apple.Mail sync alert tool path /System/Library/Frameworks/Message.framework/Resources/MailSync does not exist.
Oh well, back to the drawing board.😉