If I had definite plans to buy a DSLR in the future, I wouldn't buy a G6, you can get a smaller Powershot with a DigicII processor now, and though the lens wouldn't be as good, it doesn't make sense to me to have a kinda big camera and a big camera, i'd rather have a big one for important stuff, and a small one to carry around with me all the time.
As it is, I just wanted one camera, (and I have a film SLR if I REALLY need it,) so I went with the G6, which as it turns out is maybe a little big to lug around all the time, but I do anyway, and I've been really happy with it's performance. I bought it in the spring, if I was looking now, i might consider the S2IS, because of the much better zoom and movies. I don't have a digital video camera, so i often shoot movies with my camera. (iMovie and iDVD make it easy to assemble the movies and photos on a DVD for the grandparents). But the G6 is superior to the S2 in image quality, so it's a tough call.