studies have shown that finasteride can indeed lower sperm count, but that after its discontinuation, it tends to come back up.
studies haven't been done over the long term, though.
i've got an appointment with my GP this thursday to set up a fertility test. I'll get this done and then start finasteride. after a few months i'll get another done, and see if theres a reduction...and probably again few months after.
believe me, i share your concern and that's why i've held off starting (i've already got the propecia at home). I'm only 22, and while i have no plans of having kids in the next few years, i certainly plan on it in the long term...and this is the one thing that puts me off finasteride.