Notes is turning out to be really nice, fast and extremely simple.
Here is the finalised concept! (The Black parts mean that the part underneath them will be removed ) Sorry about the bad compression!
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I really like the idea. However, one point of advice: It doesn't "look" like a Windows 7 app. Since all I've seen so far is the UI, that is all I can comment on. Frankly, I wouldn't actually use this based on the UI alone.
Going out of your way to create a "different" type of UI so that it will stand out is generally a bad move when developing software. Since you like the "tabs on top" style, I'd recommend checking out MS Paint and Wordpad (or possibly Office 2010) for tips on the UI. This dark UI is very inconsistent with other apps that a user will most likely have installed on his/her computer, and will make the desktop with multiple apps open simultaneously look really jumbled and messy.
EDIT: I see that you've stepped away from the "tabs on top" idea. My new recommendation would be to make the top bar match the light blue toolbar in Windows Explorer (and almost every other Windows 7 app), and make the bottom bar match the large item details bar at the bottom of Windows Explorer. This way, it'll look like in actually "belongs" on Windows 7.