I took Propecia on and off for a couple of years (mostly on) and never really noticed any regrowth. However, my thinning has been almost entirely at the front of the hairline, which is apparently not something Propecia is great at regrowing. FWIW, I never noticed any additional thinning while on the medication, so it was doing its job in that respect.
I've been using Fincar for the last two weeks and am going to ride it out this time. I've noticed a slight drop in libido, but I'm trying to have perspective here and going to give my body enough time to adjust to the drug before I panic.
Since my thinning has been at the front of the hairline, I'll also be incorporating minoxidil into my regimen shortly.