Crime rates in Washtenaw County remain relatively low, although violent crime is more common in Ypsilanti. In Ann Arbor and the smaller towns, at least, it's generally quite safe to walk through town even late at night. As always, though, be circumspect, and don't take unnecessary risks.
Washtenaw County tends to have a few cases of West Nile virus each year. If you're going to be out after dark, particularly in wooded areas, be sure to take mosquito-repellent precautions, like dousing yourself in bug spray and wearing clothes that cover your bare skin.
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Beginning in 2004, Washtenaw County embarked on a plan to provide free or lower-cost high-speed wireless Internet access to everyone in the county, regardless of their location or economic status. Although the project has been held up by funding issues, the goal is for all urban and rural areas to have wireless connectivity within the next few years; 84KB low-speed access will be free, and higher-speed access will be available for a monthly charge of $35 and up. As of January 2008, 30 square miles in the county have wireless coverage.
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Ann Arbor along with its neighbor Ypsilanti is a university town with a large number of international students. This means a lot of international restaurants, ethnic grocery stores, and lots of non-native speakers of English. There are several language schools in the heart of downtown, so as you're walking down the street, you're highly likely to encounter groups of people speaking Korean, Mandarin, Spanish, Arabic, or one of dozens of other languages. Of course, there are also native speakers from all over the country, and the rest of the English-speaking world, so you're liable to hear a wide variety of accents as well. For a small town, there's a surprising amount of cultural diversity.
Also recognize that you're not far from Dearborn, home to the largest Middle Eastern population in the United States. While the Arabic population of Ann Arbor isn't nearly as visible as its Asian particularly Korean population, you may have the opportunity to meet visitors from Arab countries or locals of Arab descent.
As for the native English speakers in the area, Michigan is situated in the middle of the Northern Cities vowel shift, which in some ways has made the local accents more similar to a Canadian accent. In particular, you're likely to notice a difference in the low front vowel a as in "hat" and "ramp", which is raised and highly nasalized, and the close-mid back vowel o as in row and soap, which is fronted such that it resembles a Minnesota accent.