Sorry, late to this party, but can I still chime in?
Foundation should not be visible unless you're really, really close up. I wear it most days, but not all over my face -- just on the pinkish areas around my nose. You can still see my freckles through the foundation, and my freckles are quite faded to begin with, so the foundation must be on the sheer side.
Those who mentioned blending like crazy are right. Also, it's important to get the right shade. Usually when you can see a woman's foundation, it's because she's wearing something too dark. Err on the side of lighter than your skin tone (which can be tough for whitey white gals -- I always have to use the lightest colour in the range, and I have a friend who's even whiter than me and who has trouble finding face makeup to match her skin!).
When I say "lighter", I don't mean a ton lighter -- just a smidge -- and I can only speak for proper foundation, not mineral makeup, which I've never tried. Sheer foundation never looks chalky, even if you apply it wrong, but it can look dreadful if it's too dark.
I also agree with the others about how faces tend to look better when they are not too matte. Mine is "shiny like and apple", like Angie says, and I like it that way. If it crosses the line and starts to look greasy, as can happen in humid weather, I blot with a paper towel. Problem solved.