We do cum but it takes alot to do it right...  Alot of it is fake though.... I do agree with that.... But theres alot of women who are skilled and can do it for real...
This information is coming straight from Wikipedia.
Female ejaculation
 Main article: Female ejaculation
 Some believe that the Skene's glands are the source of 
female ejaculation.
[3] In 2002, 
Emanuele Jannini of 
L'Aquila University in Italy showed that there may be an explanation both for the phenomenon and for the frequent denials of its existence. Skene's glands have highly variable anatomy, and in some extreme cases they appear to be missing entirely. If Skene's glands are the cause of female ejaculation and 
G-spot-orgasms, this may explain the observed absence of these phenomena in many women.
[citation needed] [4][5]
 It has been demonstrated that a large amount of lubricating fluid (filtered blood plasma) can be secreted from this gland when stimulated from inside the vagina.
[citation needed]
 
  Female prostate
 The fluid that emerges during 
female ejaculation has a composition similar to the fluid generated in males by the 
prostate gland,
[6] containing biochemical markers of sexual function like human 
protein 1
[7] and the enzyme 
PDE5. When examined with electron microscopy, both glands show similar secretory structures,
[8] and both act similarly in terms of prostate-specific 
antigen and prostate-specific 
acid phosphatase studies.
[9][10][11][12] Because they are increasingly perceived as merely different versions of the same gland, some researchers are moving away from the name 
Skene's gland and referring to it instead as the 
female prostate.[13]
 
  Sexual Response
 Some women have reported that massaging the area around the urethra, particularily the Skene's gland, results in a pleasurable sensation and even 
orgasm. This has resulted in the the Skene's gland being referred to as the "U-spot" by some.
Heres a pic of the whole area:
