Occasionally, but only because my iPad 3 has a better camera than my iPhone 4. Otherwise, I would have reached for the iPhone.
In most cases it was because I needed a simple photo for Facebook or to quickly email someone, and using my phone/tablet was the quickest way to get the shot. Otherwise, I would have had to go grab one of my regular cameras (Panasonic GF2, Canon PowerShot S100), take the photo, take out the SD card, pop it into an SD reader, pop that into my computer (and if I'm out travelling, that means waiting till I get back home or to the hotel), find the photo I want, copy it to the computer, then fire up Safari, load the website, and upload it.
Or, you know, pick up phone/tablet, camera app, CLICK!, tap Library, tap Share, send to appropriate app, done.
I was one of the first people to say that cameras in phones and tablets were silly and useless, but they've come a long way. Of course they're not as nice as a "real" camera, but they sure have a lock on convenience, and the quality we get now is definitely good enough for casual posts or emails.