Christopher Guest is in the midst of shooting A Mighty Wind, the account of old folkies (played by his Spinal Tap bandmates) getting together at New York's Town Hall to commemorate the passing of legendary folk music manager Irving Steinbloom. A pseudo-doc master, who directs commercials through Moxie Pictures, Guest can be maddeningly coy when asked about the advertising process. "How does he deal with agencies and clients?" he's asked via e-mail. "I've never actually met any agency people or clients, but I've heard a lot about them," he responds. Despite his dismissive nature about the ad world in general, his approach is widely admired as having heavily influenced everything from SportsCenter to Saturn. Asked what he thinks of how the faux-documentary, seeped in irony, has become a staple of television advertising, he answers, "I didn't realize it had."