Is anyone in a long term relationship and use family planning as a contreception?

http://www.nhs.uk/Conditions/contraception-guide/Pages/natural-family-planning.aspx
i'm just looking for anyone who's got any experience about the subject, i can't use any other method of contraception for various reasons.
I just basically want to know whether it can actually work and if its hard keeping track of everything. Also has anyone had experience of becoming pregnant whilst using the method?