Just curious as to how many people are pretty sure they are about to O based on CM change...

I'm pretty sure i ovulate when i see EWCM although this month i'm using OPK's so i can be definate as i've had a little EWCM yesterday but got a negative result on the OPK so i'm not ovulating yet but soon should be

good to know, i just found this article that explains CM purpose really well.

Q. During the days before a woman starts to enter her fertile zone, before any signs of good fertile cervical mucus even, can sperm enter the cervix? Or is the cervix open enough for sperm to get in only during the fertile period of a woman's cycle? My husband and I have started to have intercourse every few days, even though my fertile period has not yet started, and I am wondering if any sperm is able to make its way through my cervix yet. I hope so, just to be ready in case ovulation happens in the next week.
A. It isn't really an issue of your cervix being "open enough" for sperm. The World Health Organization did studies looking at when conceptions occur related to intercourse. Approximately 10% of all conceptions occur from intercourse seven or more days prior to ovulation. Because some men's sperm can live up to two weeks in the woman's Fallopian Tube, women can even get pregnant from unprotected intercourse during menses, but that is pretty rare (the super sperm!).

The issue on sperm and cervical interactions has to do with mucus quality. During the non-fertile part of the cycle, the mucus is acidic which kills sperm. When your egg is ready, the mucus becomes a pH of 7-8 (which is what pre-seed is) to support the sperm. There also are fibers in the mucus. These fibers are not lined up right and are too close for sperm to move freely in non-fertile mucus. When you ovulate, water comes into the mucus gel and the fiber spacing expands, and the fibers line up. This promotes sperm transport within 30 minutes after intercourse through the cervix up to the Fallopian Tubes.

So it is fine to have intercourse prior to ovulation, BUT . . . some men's sperm doesn't live long in the Fallopian Tubes. This has been my area of research for years. In fact, for some men it may only live a few hours instead of days to a week. Therefore, if you are having problems conceiving, you want to make sure you have intercourse LONG ENOUGH through the cycle - this is a common mistake people make. Remember ovulation tests tell you when a hormone is released. The egg is then released 6-12 hours after this release and the egg can be fertilized for 12 hours+ after that. So if you don't have intercourse after you have the hormone rise and your husband's sperm are not long-lived, you will miss the right time.

heres where i found it...

http://www.storknet.com/cubbies/preconception/exje6.htm