Asher Yatzar:

This Beracha is said as an expression of gratitude to Hashem, for the marvelous structure and functioning of the human body.  In this Beracha, we acknowledge to Hashem that the properly functioning, healthy body is a marvelous gift from Hashem to man.

If one says this Beracha with proper intent, it can be a great source of Yiras Shamayim, Emunah and Bitachon.

The Chafetz Chaim and other Great Sages write that the saying of Asher Yatzar with the proper intent and from writing has the power to help one have a healthy body all of his life.  There are many people who were saved from a severe illness by saying this Beracha from a written page with the proper intent.

This is an easy way to keep down all those doctor fees!!

The following explanation is given to help you to have greater intent when saying this Beracha, most of the explanation was taken from Rabbi Schwab on Prayer - which is an excellent Sefer on Tefillah, it is available Online at:  Artscroll

Blessed are You Hashem our G-d the King of the Universe May You be increasingly recognized in the world, that more people will live their lives according to Your will.
Who fashioned man with wisdom We are created with a physical body and a Holy Soul - therefor we have a double use of (Nekavim and Chalulim).  That for every physical organ, we also have a spiritual organ.  
Hashem created man and gave him wisdom, and Hashem used wisdom to create man.  This is demonstrated in the precise balance of man's organs and functions.
He created within man many openings For each physical opening there is a spiritual one.  An example of an opening is our mouth, ears....
And many cavities For each physical cavity there is a spiritual one.  The cavities are the inner hollows that contain such organs as the lungs, heart, stomach, and brain.
It is openly known before Your Throne of Glory The angels that bring sickness to the world know the potential dangers in the body.  Our being able to exist, body (Guf) and soul (Neshama) together as a human being, shows G-d's wondrous acts. 
That if one of the organs which is closed should open (Chalulim - cavity) These are usually closed, should G-d forbid they open...
Or if one of the open ones should close (Nekavim - openings) These are usually open, such as the lungs.
It would be impossible to exist and stand before you From the time that man is born if what needs to open stays closed, or what needs to close stays open - one could not live.

When one is sick and needs to constantly go to the bathroom - he is unable to stand before Hashem in Prayer, even though he can exist in the world.

(Even for one hour) some include this verse, some leave it out since one can live a short time, but not long if his body's organs malfunction)
Blessed are You Hashem who heals all flesh we thank Hashem for healthy working bodies that he gives to ALL his creatures.
And acts wondrously Here we talk only about man - That Hashem has attached the highest form of spirituality (Neshama) to the lowest level of physicality (Guf - one's physical needs).  These two complete opposites stay together even though we have many openings in our body!


(Adapted from - Rav Scwab on Prayer and other Seforim based on the importance of this Beracha, Rav Paysach Khron audio recording, Artscroll Siddur, Erachim)