i have never tripped alone, but i'm planning on doing it sometime in the near future.
my friend tripped alone today, though he wasn't totally out of contact with people...he was talking to me on the internet. he had a good time, i think, though the 'shrooms, he said, weren't that potent.
i think tripping alone would be a good way to explore yourself and it could be a very enlightening experience.
i think though, that if you were to trip alone, you should do it actually ALONE, meaning in an empty house or something, and have a phone or internet or something at hand so that you could contact friends if something started going wrong.
terrence mckenna said you should eat 5g alone, so hmm....