http://en.wikipedia.org/wiki/Prostate_massage there's some wiki info for you guys lol.
Also, from a medical website :
Prostate Gland
The prostate is a walnut-sized gland that lies below the urinary bladder and surrounds the urethra. Along with the seminal vesicles, the prostate gland produces a fluid, called prostatic fluid, that contains, protects, nourishes, and supports the sperm. The white, sticky fluid originally from the prostate forms most of the volume of the semen. The prostate has no known function other than reproduction.
The prostate grows throughout life. This growth often causes a blockage in the urethra that affects voiding with such symptoms as urinary frequency, excessive voiding at night (nocturia), urgency of urination, and weakening of the urinary stream. This enlargement of the prostate, called benign prostatic hyperplasia (or BPH), can be treated with medication or various surgical procedures, such as laser or microwave therapy.
The prostate is also the source of a prostate specific antigen (or PSA) that is used as a blood test to detect prostate cancer.