Traxdata,
I faced a similiar dilemma to you last year and quit propecia after three years of usage. Propecia had provided me with steady results on the hair front, but the at an increasing mental and physical cost with subsequent effects on my personal, social, sporting and working life. Depression, mental fog, anxiety and reductions in libido were my chief side effects. I was also concerned about the long term impacts which may have yet to manifest themselves amongst users. I wound down usage over a six month period, which is something I think you should consider, and finally quit in April 2006.
I am delighted to report all side effects gradually disappeared over a three month period and I experienced no extreme sheds. I replaced Propecia with Fluridil and topical spironolactone, and whilst overall hair density appears to be reduced, I am happy overall with the results.
Good luck with your decision, but from my experience, you are taking the right course of action.