In July of this year (2001), Rick Mercer left This Hour... so that he could focus more of his attention on his newer show, the also-hilarious Made In Canada. This is kind of a shame, since Mercer was widely considered to be the sharpest member of the cast.
Starting with the Fall 2001 season, however, another of Canada's finest, Colin Mochrie, has stepped in to fill Mercer's spot. Seems like the guy's on nearly every channel these days. If you've ever seen an episode of either the Brit's Whose Line Is It Anyway?, or the American version thereof, you'll recognize the face.
Mochrie's goofy improv style of humor is obviously a big shift from Rick Mercer's more deadpan and cynical riffing, but he's still top-drawer talent, and added to the show's news satire formula you could hardly go wrong.