I've got both the S90 and G11 and have been considering upgrading one or both to the S95 or G12. I was considering the Nikon P7000 since my SLR gear is Nikon (D70, D300, 3 SB800 speedlites, several lenses) but I want the swivel screen the G11 and 12 have.
I took the G11 to Maui back in March and both to Punta Cana in November and am very happy with them. Before getting these I was always lugging around a dSLR on vacation because I wanted to get better than P&S image quality. The only time I really missed my dSLR was when I was whale watching in Maui where the extra zoom was missed, but I still managed to get some decent shots.
When I first got them I was initially not happy with the white balance issues when using flash in incandescent lighting due to the warm (yellowing) color cast, but unless you use the proper gel over your flash you'll get this with any camera. I usually shoot in the Vivid color mode but switch to neutral when shooting in incan lighting and the color cast isn't as bad.
Both are great cameras offering full manual control and each offers features the other doesn't have. For example, the S90 has the Nostalgic mode within the Scene (SCN) menu. It also has the faster lens at the wide open end - f2.0, compared to the f2.8 on the G11. All this means is that wide open, you'll get one full stop more than the G11. This is good for low lighting/no flash shots as it allows you to get decent hand-held shots.
The G11 has the advantage of the swivel screen which is great for candids and getting shots at weird angles. It also has the 5x optical zoom compared to the 4x of the S90.
Besides the addition of 720P HD video capabilities on the S95 and G12, I like that they added the 2nd strap attachment point to the S95 like there is on the G series, allowing you to hang the camera around your neck or shoulder without it dangling around as much.
If you go with the S90/S95, get Richard Franiec's grip. It makes a world of difference in the ergonomics of the camera. I'd also recommend getting at least 1 extra battery for them (I buy at least 1 extra battery for all of my 8 digital cameras!). I also always buy screen protectors for all of my electronic devices with LCD screens off ebay.
Good luck with your decision! They're both great cameras.
Here are some sample G11 shots from Maui.
Using the built in Neutral Density (ND) filter on the G11:
Hand-held night shot:
Beautiful color: