Having waded through most of this 2 1/2 year long thread, I don't see the real meaning of non-denominational (though godrocks above has much of it).
I believe that most non-denominational churches are founded on the principle that they reject the authority of man's rules (denominational hierarchies) in favor of God's rules (the Bible). This is a positive definition but not a definitive one. Since in a nondenominational church there is no denominational hierarchy to interpret the Bible for us, we are responsible to study it on our own. It becomes the guidepost for everything in the church, from governance to teaching. This is also called a "Bible based church".
If the church is to be truly inclusive, this often means only the most basic, core Christian tenants that most if not all can agree to are the churches founding tenets. The nature of God, the divine and inerrant inspiration of the Bible, and the core Salvation message are the starting points. If the church is composed of mostly one denomination or has a strong charismatic Pastor it may move in a slightly more unified direction regarding other portions of the Gospel (that might or might not parallel a formal denomination). More likely, it heavily promotes individual spiritual growth and personal Biblical understanding above non-core doctrinal unity.
I find non-denominational churches to be more personally challenging and fulfilling because of this, but your mileage may vary.
Thanks,
Tim