Do you you know God or just know about God? That's the concern of J.I. Packer in the opening chapters of his excellent book, Knowing God ($2.99 for Kindle right now!). He lists four evidences explained through the book of Daniel of the effects the knowledge of God has on a person (pp 27-32). I'll give the four and quote from each of Packer's explanations, but I encourage you to read this section and the whole book. It's rich. I forgot how really great it is.
1. Those who know God have great energy for God
"Those who know their God are sensitive to situations in which God's truth and honor are being directly or tacitly jeopardized, and rather than let the matter go by default will force the issue on men's attention and seek thereby to compel a change of heart about it--even at personal risk."
"People who know their God are before anything else people who pray, and the first point where their zeal and energy for God's glory come to expression is in their prayers."
2. Those who know God have great thoughts of God
Packer takes a brief survey of the book of Daniel, ending by saying, "[God] knows, and foreknows, all things, and his foreknowledge is foreordination; he, therefore, will have the last word, both in world history and in the destiny of every man; his kingdom and righteousness will triumph in the end, for neither men nor angels shall be able to thwart him."
"These were the thoughts of God which filled Daniel's mind."
3. Those who know God show great boldness for God
"They may find the determination of the right course to take agonizingly difficult, but once they are clear on it they embrace it boldly and without hesitation. It does not worry them that others of God's people see the matter differently and do not stand with them."
4. Those who know God have great contentment in God
"There is no peace like the peace of those whose minds are possessed with full assurance that they have known God, and God has known them, and that this relationship guarantees God's favor to them in life, through death and on forever."