@Wuffer, if you read the rest of the thread, you'll see that I said I was being sarcastic and that I'm a proponent of finasteride. Obviously, finasteride will not cause your penis to shrink a couple of inches.
@swingline, the first and third links you posted say that it is being looked into whether finasteride causes Peyronie's Disease, but I don't see them saying definitely whether there is a definite link between them. The second link notes that 0.13% of finasteride users with side effects develop Peyronie's Disease as a side effect. Let's say that rather than 2%, 20% of finasteride users have negative side effects. That means 0.026% (20%*0.13%) of finasteride users get Peyronie's Disease.
Here is an article from the NYT that mentions 5% of all males develop Peyronie's Disease:
http://www.nytimes.com/2012/06/04/health/treatment-for-peyronies-disease-shows-promise.html
Thus, if 5% is correct, then there is a MUCH LOWER incidence of Peyronie's Disease among finasteride users. The article does mention that estimates vary and I believe more studies would need to be done, but at this point it seems like there is no connection.