While I use My Days to track my wife's cycle, you can have improved accuracy using an LH strip. It's a "pee in a cup, stick strip into pee for three seconds, let dry for five minutes" test.
The beautiful thing is that the LH surge happens very reliably, 24-48 hours before ovulation. (see the third chart in this link and note how narrow the blue peak is compared to the other charts: http://upload.wikimedia.org/wikipedia/commons/c/c8/Hormones_estradiol%2C_progesterone%2C_LH_and_FSH_during_menstrual_cycle.svg )
I've also read (Amazon reviews, so take with appropriate amounts of salt) that if a woman has polycystic ovarian syndrome, she may not ovulate, even if she menstruates. The LH surge can tell her when she actually ovulates.
Using the LH strip in combination with My Days, you can reliably avoid or become pregnant. After a few cycles, you can tell whether My Days is correctly predicting ovulation (my wife is usually right on or a day late). Since sperm lasts up to five days, and there's some natural variations in the cycle, we generally avoid 8 days before and four days after ovulation is supposed to start. No condoms, no pill, no spermicide, and still no babies, four years running.