[Nyororin]

I`m female and have lived in Japan for 10 years... And have done my fair share of traveling.

I would agree that as long as you use common sense Japan is a very safe country. If you are using the same level of common sense that you would use in your own country, even more so. I could walk around the city at night and not feel in danger at any point, and have even gotten stuck a few times and ended up staying outside a station through the night. The worst that has happened would have to be having drunk guys invite me to accompany them. (With the obvious connotations.)
Other than that... once, on a back road by a river (very secluded) late at night, and old homeless man (clearly mentally ill) tried to catch me. The guys who I`d decided to take that road to avoid in the first place - a motorcycle gang (which ended up including my friend`s boyfriend, but I had no way to know from a distance) - ended up coming over and giving me a ride home.

If you don`t speak Japanese, I wouldn`t worry at all about dialects. Even MMM`s example of Touhoku isn`t nearly as bad as he gives the impression of it being. For a native speaker, they wouldn`t really hit any problems unless they were talking to someone very old. There are virtually no Japanese who speak entirely in what would be considered a true dialect. It is more accent with some dialectal words.

And a random fact out of nowhere - apparently the prefecture that has the most pronounced non-standard "dialect" use in the normal population is Fukui. It is also supposed to be one of the oldest forms of modern Japanese still in regular use, carried up there by migrants from Kyoto and little changed over time.