Dude, I doubt it's any consolation, but I've been experiencing the same type of thing.
I always hear people on the boards talking about "sheds" where they lose 40-50 hairs in the shower. Since June, I've been losing around 200-250 hairs every time I wash my hair.
Like you, I also don't have noticeable thinning in the eyes of the average person (at least I don't think so...). Whenever I tell people I'm losing it, they say things like "What are you talking about?" Last month, one of my roommates actually told me he envied my "thick hair." I can tell that my hair is thinner than it once was, but I'm amazed it isn't a lot worse than it is.
Like you, I've also been on Propecia for over five months. I'm working on the sixth month right now. The only good news I have to report is that, in the last week, I've lost significantly less hair in the shower (although it still comes out when I run my hands through it, and I still find it on my pillow and on my shirt). I'd say I'm losing more like 50 hairs in the shower, as opposed to HUNDREDS. Maybe yours will decrease soon, too.
Just thought you'd like to know that there's someone out there in a similar situation...and who may be experiencing a turnaround...
Best of luck!