I've heard people on this forum say its a good thing to hold off on the minoxidil and use Propecia to maintain what you have, then when it starts to wear off jump on minoxidil to get a few extra years out of it.
I got on both of them right away, minoxidil works great.
It's a pain in the *** though, and a long-term (lifelong unless a "cure" for male pattern baldness comes about) commitment. Twice a day, has to sit on your scalp for 3 hours before you can wash it off.