I live in Frogtown. Some areas can be rough but there are a number of good things about my neighborhood: convenient (close to highways, bus lines AND the Lightrail line is going to be built on University Ave very soon), Asian restaurants, cheap houses. It is a lower to middle income neighbiorhood so please don't compare it with Uptown Minneapolis or Summit Ave (Saint Paul).
It is not dangerous but yes I do see some activity sometimes (I assume drugs).
I am white female in my 30s and I walk and take public transportation every day (including dark hours). So far without any problems.
If you want to buy a house you should seriously consider this neighborhood.
here's a good link to check out:
http://www.greaterfrogtowncdc.org