Top 10 on why guest hosts are bad idea

David Letterman was in the recovery room, what - a day? if that? - when someone started floating the idea "wouldn't it be great if Johnny Carson came out of retirement and filled in while the host of the CBS 'Late Show' recuperated from bypass surgery"? By Tuesday the idea was in full snowball. Rosie O'Donnell and the host of TV's hottest show - Regis Philbin of "Who Wants to Be a Millionaire" - offered themselves as guest hosts. Readers have been sending me e-mails, each one straight out of the zeitgeist. Forget it, everyone. CBS has put the kibosh on the guest-hosting idea. "Our first and primary concern continues to be Dave's health and we're thrilled that all signs point to a speedy recovery," the network said. "In the meantime we plan to provide viewers with the best of Dave in repeats." For once, I'm with the pinheads at the network. Bringing in guest hosts for Letterman is one of those ideas that sounds like a can't-lose - that is, until somebody actually tries it. In the spirit of the Letterman show, here's the top 10 reasons why it doesn't work. Drum roll, please: 10. This isn't baseball. The idea of guest hosts is reminiscent of "The Tonight Show" during Carson's reign, but many of us are more likely to recall the time in the late 1980s when Chicago Cubs announcer Harry Caray was recovering from a stroke and superstation WGN scored a hit by hiring celebrity guest announcers to call the games in his absence. CBS, however, is not under any decree to keep playing new shows while its star is on injured reserve. The season will go on regardless. And CBS may even sell a few more concessions: "Late Show" repeats this week have been scoring nearly as high in the Nielsens as recent first-run shows. 9. Reruns allow Letterman to re-endear himself to former fans. Viewers who stopped watching Letterman over the years - since 1994 he's lost nearly half his audience - may be feeling a twang of sympathy for him. Perhaps they're checking out the reruns for old times' sake. What could be a more pleasant surprise for these wayward fans than to see the Dave who reinvented himself about 1994 - bespectacled, definitely starting to look his age, yet invigorated, brighter, funnier than he'd seemed in years? As he has done throughout his career, Letterman had caught another wind. The comedy seemed sharper. He was booking better guests. This is the Letterman CBS wants as many viewers as possible to see - and, one would think, so does Letterman. 8. Guest hosts would be more trouble than they're worth. No matter who is seated in Dave's chair, there would be so much to learn, both for the host and those running the show, that the results probably would not be very satisfying. Letterman has one of the most loyal and talented staffs in the business. They have learned to tailor their jobs around the quirks of their boss. But only a few of today's celebrities have ever sat behind a late-night talk show desk, which means Letterman's staff would be walking them through the basics every night, coaching in ways they've never had to before. 7. Guest hosts would dilute the comedy. With this sudden hiatus, Letterman's staff has been given the rare gift of time to write, shoot and bank material for future use. A guest-hosting system would blow that chance, since monologue jokes and comedy bits would be needed every day for the fill-ins. 6. Dave isn't Johnny. In his 20 years as a talk show host, Letterman has always wanted the stage to be his. Unlike Leno, Carson and Paar, he almost never allows more than one guest at a time by his side. And since it is Letterman's company, not CBS, that owns "Late Show," any decision on a seat-filler would have to come from the man who has never allowed his seat to be filled by anyone else. 5. Johnny isn't Dave. Since signing off for the last time nearly eight years ago, Johnny Carson has seen his television legacy swell to biblical proportions. He's now seen as a Moses standing at the other end of the Red Sea: All he has to do is show up and the parted waters of American culture will seal up once again. Well, maybe for a night. And after the novelty wears off, then what? Put yourself in Johnny's shoes. Would you fly to New York and take over a studio you've never seen before? For a show that moves at twice the speed that yours once did? Carson has already engineered one perfect departure; why tempt fate trying another? 4. We went through this last time. As NBC learned when it tried to replace Letterman in 1993, very few people are talented enough to do a late-night talk show. Chevy Chase, Whoopi Goldberg and Dennis Miller tried and failed. 3. CBS would be nuts to want guest hosts. Letterman's numbers have not exactly been boffo in recent years, but "Late Show," even in reruns, draws impressively from that pool of young male viewers that CBS has a hard time reaching at any other time. Make no mistake: Advertisers keep the networks in business, and advertisers want shows that skew young. Now imagine five nights of Johnny Carson, or Steve Allen or even Regis Philbin. Nostalgia buffs would love it, but a lot of younger viewers wouldn't - and CBS would hate that. 2. Not everyone has Dave's best interests in mind. The media don't write about the "late night wars" like they used to. They want fresh meat. Bringing in guest hosts would be just the ticket. Soon we'd all be arguing over which guest host was the best and which one might be "the next Dave." More heart medicine, Mr. Letterman? And the No. 1 reason guest hosts are a bad idea ... 1. Repeats will speed Dave's recovery. In 1988, during a writers' strike that dragged on for months, Letterman had to sit by while NBC aired endless repeats of his show. Finally he went back on the air with no material other than what he had scribbled down earlier in the day. (By the way, they were some of his greatest shows ever.) Trust me, after a few weeks of watching himself on TV - counting every imperfection and screw-up he makes - Letterman will work himself right back into fighting shape. Until then, the rest of us should just sit back and enjoy the show. Again. @ART:Photo (color) @ART CREDIT:CBS