I guess it's a matter of intent: if I already know I'll want to share the pic I'm about to take I just fire up Instagram, otherwise I use the standard camera app.
On a related note: the Google+ Instant Upload feature does even 'better'. From the G+ website: "All photos and videos taken with your mobile device are uploaded to the From your phone album. These photos and videos are only visible to you unless you share them." That's even more frictionless sharing, but not in a way I like: it freaked me out when I inadvertently turned this on.
That actually sounds reasonable -- you can log-in, decide which photos you want to share and delete the rest. Unless you don't like it using bandwidth or don't like google itself having access to all your stuff.
On a related note: the Google+ Instant Upload feature does even 'better'. From the G+ website: "All photos and videos taken with your mobile device are uploaded to the From your phone album. These photos and videos are only visible to you unless you share them." That's even more frictionless sharing, but not in a way I like: it freaked me out when I inadvertently turned this on.