I almost exclusively brew fruit beer. Part because I'm living in Hawaii, and part because it's hard to find a good one in the stores/bars.
If you want a fruit aroma, you can steep in your boil.
If you want a fruit body, which I much more care for, you want to dry hop in the secondary. IMHO, if you're adding to the secondary there is enough alcohol and co2 to protect the wort from comnatmination If you use fresh fruit, rinse it and make sure the fruit isn't rotten to begin with. Don't worry about it too much, making beer is supposed to be fun.
If you do used commerical fruit, they usually add sugar/corn syrup to perserve the fruit. If that is the case, your ABV will go up about 5% or so, depending on the amount of sugar in the fruit and the amount of fruit used in the secondary. The additional alcohol, once completely fermented, will make your beer sour.
Since this is unavoidable, you need to backsweeten the beer at bottling. This can be done with Lactose (available at your Homebrew store) or splenda (available at your grocery store.) For my wheat beers, I use lactose as it adds body as well as sweetness. When I made a light fruit beer (mango ale) I opted for splenda as lactose would cloud the beer.
My experience has shown that a high ABV beer (i.e. fruit in the secondary) will result in a lighter head if you use the conventional 3/4 cup of priming sugar. To correct for this, I add another 2 T. of priming sugar at bottling...this has helped.
My last caveat is to always use a 3rd fermentation to avoid gushers/bombs. I didn't and wasted a whole batch which gushed on opening. A one week wait is a very cheap price to pay for the best fruit beer you ever had.
Good luck and may the yeast be with you!
