User Activity

Taking a vacation soon and expect to be doing quite a bit of shooting indoors in low light.  Assume flash isn't always allowed or convenient.  Anyone have experience with the G15 in these situations, and what settings have worked well for you?
Just got a Powershot S110 to be the "more pocketable" companion to my G15.  The 110 has a Program mode, but I can't find any way to shift the program.  If there is no program shift, how is this any different/better than Auto?