I backpacked in Guatemala alone was back in 2006. I felt pretty safe. You need to take your standard precautions.
But then, I'm a brown skinned, dark haired woman from a third world country (not Latin America) who just happens to live in the US. Most people in Guatemala did not look at me twice
Jokes aside, I enjoyed my trip there - the people are warm and friendly - but very poor. As long as you don't act like a typical tourist, you should be fine.