I have a mid-2012 Macbook Pro. I've noticed that when I close the lid and it (supposedly) goes to sleep, it's actually periodically waking and connecting to the wifi.
The reason I know this is happening is because when I open the lid I can look back through my LimeChat IRC logs and see the times at which it has reconnected.
For example, I shut the lid at 19:30 last night and opened it again just after midnight. My LimeChat logs show that it reconnected exactly every 56 minutes while the computer was supposedly asleep.
My currently running apps are Dropbox, Chrome, Skype, LimeChat, SublimeText and Terminal (no remote connection). Bluetooth is switched off.
Any hints? Is there a chance that an app such as Dropbox is causing it to wake?