Decided to share my experience with the battery drain.
I got my Nexus 7 about a month ago. At that time in average battery drain was about 11-12% per day (24 Hrs) in sleeping mode (I didn't keep it idle for 24 Hrs, but easy to calculate it after a night sleep). It wasn't great (not the promised 300 Hrs, but acceptable).
Then I installed some applications, accounts, etc. The daily drain in sleep mode raised to 16-17%. Not great.
After installing Skype (it runs even if you try to exit it, until you kill it as a process) the train increased to 24%!!! Which was totally unacceptable.
Switching off Wi-Fi, GPS didn't help. Even when sleeping Wi-Fi still was ON (in spite of the option to shut it of when sleeping) - I had solid bar in the battery chart.
I started searching forums (especially this one) and decided to follow some advises.
After disabling all possible Google services (like Books, Movies, Magazines, Current, etc.), deleting weather widget, switching off location reporting in Maps, disabling all possible syncs and notifications I've got 4% battery drain per day (24 Hrs)!
Now I use the battery, but not some Google apps.
Well, it's time to switch ON some notifications or services which I really need, but the bottom line is this - it's achievable to significantly reduce the battery drain. I think the main culprits were Google services (Magazines, movies, etc., which I anyway replaced with another apps I liked more).
Hope it will help someone.