Sometimes I use characters as inspiration for what my sim will look like, or for their name - but, I don't name them (first & last) after the character(s) and then play them as the character. Like, I had a sim named Harper Helo (named after Helo from Battlestar Galactica) but it was a female sim who was a reporter. So, just the name in that case. I do celebrities in CAS sometimes for fun, but I feel the need to tweak them and make them my own if I'm going to use them in a game.
Edit: Oh yeah, kinda funny - I created a Christina Hendricks look-a-like sim, and then I changed her all around to make her my own and then a few days into simming her I realized she wound up coming out looking a lot like Geena Davis. O.o
