Ali G was something of a revelation here in the UK about 10 years ago, when he was a sketch on a late-night comedy show. After a while, his potential victims had worked him out, and by the time he got his spoof talk show, everyone knew the joke.
I'm not much of a fan of Sacha Baron-Cohen. To be fair, he appears nowhere near as smug as the utterly charmless Ricky Gervais, who also got his break on the same show.
IMO, of course.