Personal experience as proof for the existence of a god has major flaws with it. The first flaw is the obvious one that it is personal and as such no one else was around to see it. However their is an even more important aspect to this and it has to do with false memories. A great article dealing with false memories has been recently published on Nature if you want to read why the legal system is now sometimes doubting peoples eye witness accounts.
False memories are just that the are not real, but created. These false memories can be either created by a persons imagniation, or they can be implanted their by psychologists/preachers/parents/etc. This phenomena is nothing new, as some children will maintain they have seen fairies or some adults will maintain they have seen UFO's........ or theists who claim to have had a personal experience with a god. All of these sightings/feelings/smells are based on natural phenomena that gets altered in your brain to become something else. For example meditation can lead to a sense of euphoria which can be attributed to an increase in oxygen in the blood (link, link, link). Or when you are praying, which is a form of meditation, and you get euphoric due to a message from god its your brain playing tricks on you. Its not that I want to be an argumentative person, but there is no way I can just accept a personal experience when there is no other verifiable evidence to back it up. I would not trust a scientist who told me some scientific evidence that does not sound rational, I would require evidence. So why do people feel insulted when I ask the same to explain their personal experiences.
I used to have a tagline on my personal e-mail that read "Its not that I don’t believe you, its just that I can no longer ignore the facts." If courts are starting to take memories into question, why should I believe your personal experience unless you can back it up with verifiable evidence. More importantly why would you want to believe in something that has no verifiable evidence.