i was with a guy who was 8.5 and as thick as a beer bottle. It took me forever to accomodate his length and girth completely, I had to work my way up to his size with prgressively larger toys/dildos.
Once I got to where I could take 8 inches comfortably (once i "warmed up," which took a minute or two) i absolutely loved it. I loved the pleasure, the pressure, that feeling of beeing massaged from the inside, and the feeling of fullness to the point of bursting. I wasn't able to take that last half an inch unless he forced it.
Most girls that I've know have told me similar stories, that they max out at about 8-8.5 inches, which is why I really find...doubtful some of the claims of accomodating 15"-17" completely.