I thought I'd add in my two cents, since I've used posemaniacs before.
The body is a funny thing. It moves in ways you wouldn't expect it to. Skin falls in places you wouldn't expect, because of angles or fat or sag. A sense of the human skeleton is great, but there's a movement to the human form that it won't give you, and while posemaniacs is a decent tool for looking at the human body and figuring out what is going where, it can't do curves and movement justice.
I've gotten a lot better at anatomy in the last month doing fifty gesture drawings every week (which is brutal if you haven't gotten form down, I know). There's a few sites out there that will flash a photograph of a model instead of a render and hold it there for a length of time, then switch it up. Try using this one: http://lovecastle.org/draw/ Block out the major shapes, and get a feel for movement and gesture. Anatomy is never as static as books and guides make it out to be.
And good luck! :)
My ImagineFX sketchbook: http://community.imaginefx.com/forums/thread/398286.aspx