Few experiences are as humbling for a music critic as reading through the lineup of the annual CMJ Music Marathon, now in its 26th year, which runs tomorrow through Saturday. Just when you think you’ve turned over every rock, listened to every record, and read through every indie-rock blog, here comes CMJ again to remind you of the astonishing scope of your own ignorance. Where do they find these bands?

In our defense, this year’s marathon is set to be the biggest CMJ ever, up 10% over last year, according to founder and CEO Bobby Haber. 1,050 bands (4,300 applied) will play 50 clubs over five days (up from four last year). There will be more than 100 daytime industry panels. And this year’s CMJ Film Series will include the New York City premiere of “Borat” (which has already given inspiration to countless Halloween partygoers throughout the city) and an appearance by Noel Gallagher for the world premiere of “Oasis: Lord, Don’t Slow Me Down.”

For the press, CMJ is less a marathon than a relay race, as teams of critics fan out to cover as much of the event as humanly possible and then share notes. But even as the long-running event reaches new heights of unwieldiness and obscurity, it faces fresh challenges, particularly from the rise of Internet taste-makers and upstart indie festivals.

This isn’t the first time CMJ has tangled with new technology. In 1999, the company — which also includes consumer and industry publications — was bought up by Rare Medium Group, one of the hotshot design-developer/incubator firms (like Razorfish and Sapien) whose bluster far outstrips its bottom line. Among Rare’s ambitions was to build what Mr. Haber calls the “quintessential galaxial Web site” for everything music related, including an artist services platform that would allow fledgling bands to build a homepage, develop an online fan base, share their music, and get discounts on insurance and gear. (Rare flamed out before the product was ever launched.)

Another thought in those heady dotcom days was to build out the event side of the business. In 2000, CMJ hosted single-day, multi-venue events in Atlanta, San Francisco, and Seattle. Another was planned for London. In this way, CMJ anticipated the transition from touring alt-rock festivals to site-specific indie-rock ones like Coachella Music and Arts Festival in California, Tennessee’s Bonnaroo, Pitchfork Music Festival in Chicago, and Cincinnati’s Midpoint Music Festival. CMJ has recently resuscitated the idea, albeit in a dramatically scaled down form, with CMJ Rock Hall Music Fest, an event cosponsored with the Rock and Roll Hall of Fame in Cleveland, Ohio.

For all the trouble the major labels are facing with piracy and the decline in CD sales, indie rock is thriving on the Internet and making inroads into films, television, and the upper reaches of the Billboard charts that would have seemed unimaginable a decade ago. “The perception is that the opportunities for independents are broader than they’ve ever been,” Mr. Haber said.

CMJ has positioned itself as a go-between for corporate America as it tries to garner a little indie cred. They’ve run programs with Coke, Key Bank, the U.S. Navy, and Zig Zag cigarettes. Along with the usual lineup of music-related businesses, Puma and Donna Karen are involved in this year’s music marathon. But CMJ may not be quite the gatekeeper it makes itself out to be. It has ceded much of its trend-spotter and taste-maker functions to Pitchfork Media and MP3 bloggers. MySpace has essentially pulled off the galaxial music portal that CMJ envisioned it might become in the late 1990s.

What’s more, Austin’s South by Southwest, once CMJ’s country cousin, seems to have supplanted it as the place where on-the-verge bands go to get famous. When I asked Mr. Haber about the groups CMJ has helped break, he rattled off an impressive list: R.E.M. in 1982, the Red Hot Chili Peppers in 1985, Green Day in 1993, and the Black Eyed Peas in 1997. But the Killers, who signed a worldwide deal with Island Records shortly after the 2003 marathon, were the only recent success story he could think of. SXSW has been far more instrumental to the success of current indie darlings like Arcade Fire, Clap Your Hands Say Yeah, and Tapes N Tapes.

Still, CMJ prides itself on the opportunity it gives unheralded — and in many cases, unheard of — bands to play the world’s biggest music city. “Some band playing at Southpaw at 4 a.m. could be the next U2, “Haber says, ever-optimistic as he looks forward to another festival. “I doubt it, but it could be.”