A friend has this camera. The G6 is a great point and shoot. But like many people who go from lower-end/older cameras (that includes P&S as well as DSLRs), you need to understand how to utilize the more advanced cameras.

Are you shooting macro or normal? If macro, are you switching into macro mode? When you are focusing, what does your camera indicate? If I remember correctly, the G6 gives you a steady green light next to the viewfinder on the back of the camera when focus locks. Also, the AF frame should turn green. If you are getting a locked indication before taking the photo and it's still coming up out of focus, then you have 1 of 3 problems I can think of:

1. You do not have the subject in the focus point. If the focus point locks on to something in front of or behind your subject, that's where the camera will focus.

2. You are changing focal length after you lock the focus or moving. That one would be obvious, some I'm doubting that you're doing that.

3. There is something wrong with your camera. You should contact Canon.

The G6 has one of the coolest AF focus points I've seen. You can move the AF box around the middle 2/3's or 3/4's of the screen to focus on what you want. Also, have you tried switching the camera into Manual Focus mode to see if you still have the same problem?