Someone at the Nanowrimo workshop I taught today asked me what I thought about using swears in writing, and we all discussed it for a long time. My opinion may be biased since I am a Mormon and I don't swear, but I think swears should be limited.
A lot of people insert them for a 'shock value' or to make it seem more cool, but it can often be unnecessary and it really does change what your reader's view on the character is. People say you shouldn't swear at a job interview because it can affect your chances of getting a job. A character who swears a lot will be seen to have more of a temper and less control. A character who doesn't will seem the exact opposite. It's just like how a character who says "I ain't shootin' no one," seems very different than another who says "I refuse to shoot anyone." Your character's language matters a lot.
Swearing too much will bog down your writing and make it heavy. If you swear less in your writing, the times you do swear will have more of an impact and stand out more. You will be able to communicate emphasis or anger a lot more clearly if a character who rarely swears begins to do so.
Another thing you want to consider is your target audience. If your writing is meant for children, swears would not be widely accepted. If you're writing for teenagers and adults, it should be fine.
I guess what it boils down it is use swears when it's appropriate. (I know of plenty of Mormon authors who use swears in their writing because that is what a situation called for.)

Feel free to state your own opinion, ask questions or suggest topics for me to cover.