I have owned and used the S70, then the S80, and now the G7. The G7 is better than the other two, by far, both ergonomically and for IQ. The only plus for the S80 is the "28mm" wide angle, but the lens quality is less good.
I changed my S70 for an S80 and slightly regretted it - it was no better optically and slightly noisier, but did have a better screen. It did not have RAW, and used SD cards so in some ways I felt it had not been a good "upgrade". Then the G7 came out and it was everything I needed in a "compact" - except possibly the 28mm - and only very slightly bigger than the S70. Obviously it also has no RAW and uses SD - but now I've accepted that is the status quo with the compact Canons.
I'm a 5D user and find the G7 a good fit for me when I want a compact, e.g. informal family shots, skiing, keep a camera in the car etc.
Oh, and yes, if you like large prints, just wait till you see what a G7 can do in terms of stitched panoramas or mosaics, with good software like Autostitch or Autopano Pro!