Yes we've been using it for almost 10 years.

When we were ttc for DS (who's now 9 1/2) I came off BCP and my cycles were all over the place. It also took us 7 cycles to get pg. I decided that since it was not so easy to get pg that we would just use FAM (a good book is "Taking charge of your Fertility" by Toni Wechsler, she describes using FAM for both ttc and birth control).

After DS was born we successfully used it until deciding to ttc for DD. We got pg first cycle. DD is now 7.

I should mention that we did have an oopsie 18 months ago that ended sadly in m/c, but apart from that we have used FAM successfully (just use condoms on your fertile days and make sure you keep checking).