FWIW, I have the 7D and 5D Mk II, both very similar body dimensions and weights. My wife and I like to go out and do photography together, and she shoots with a G12.
I often offer her the 7D or 5D when I'm using one of them, but she finds them heavy. She likes to use a swivel screen (and they definitely do have their advantages IMO) and when she decided to get an SLR, she looked closely at the 60D, 600D and the Nikon D5100. She also wanted just one lens that did it all.
The 60D was rejected on size and weight - it's too similar to the 7D for her. The Nikon was rejected because the 600D seemed quicker to focus and she was more familiar with the menus, being similar to the G12. So she ended up with the 600D and paired it with an EFS 18-200mm. She loves it. Now that combination is almost half a kilogram lighter than my 5D Mk II with a 24 - 105L lens (I'm comparing the two as main walkabout setups we use.)
So if you're after an SLR with a reduction in weight, the 600D is a good option.
But before you go out and get one, if you don't have a pocket sized camera, take a quick peek at the G12. That's an amazing little camera and there are many situations where I'm not comfortable having an expensive camera on show, or don't want/need to carry a big DSLR, and for that the G12 is perfect.
Hope that helps!
James