Thanks R2R for expounding on your thoughts...it cleared things up for me and does not require additional explanation.
While I agree that Paul had a vision problem, I don't think we can safely assume that it was his thorn in the flesh. If you have had a splinter before, you know that while it can be very painful, mostly it is just annoying. It reminds me of the expression 'a burr under your saddle' which implies something that provokes a negative reaction.
I also agree that there is no 'formula' for physical healing, but I do think we should seek God's will for it. Quite often, God chooses not to heal regardless of our faith. It is irresponsible (and unscriptural) for ministers to blame a person for a lack of faith when they are not healed! There are definitely times when the true 'miracle' is not receiving the healing and still staying faithful to God.