BALTIMORE — Side projects have long been seen as just another tent in the music industry circus. But what happens when the sideshow becomes the main attraction?

That's the problem (if you can call it that) currently facing Cee-Lo and Brian "Danger Mouse" Burton, a.k.a. Gnarls Barkley. With sales of their debut album, St. Elsewhere, surging toward the million-copy mark, what originally started off as a one-time collaboration has suddenly become one of the most talked-about projects of the year.

And naturally, fans and suits alike are now wondering when we'll hear new music from the duo. Which doesn't exactly bode well for any of their other projects, like Cee-Lo's long-delayed Happy Hour (see "Cee-Lo, Jazze Pha Host Happy Hour, And Ciara, Pussycat Dolls Stop By"), or whatever it is Danger Mouse is working on these days.

But fret not, Gnarls fans (and invested shareholders), because while both halves of Barkley make no qualms about their desire to keep multiple irons in the fire, they're also getting down to the business of making a follow-up to St. Elsewhere. Just don't ask them when it'll be finished.

"We've started to throw some ideas around, and we've started on some rough demo stuff. But it's still a little ways away," Danger Mouse told MTV News backstage at Saturday's Virgin Festival in Baltimore (see "Chili Peppers, Who, Killers Help Virgin Fest Make Its U.S. Debut"). "But we want to make the record sooner rather than later — just go in there and continue what we're doing. We definitely don't want to make [the next Gnarls record] based on our reactions to what people are saying about this album."

Mouse went on to add that while the success of St. Elsewhere has been pretty mind-blowing, he'd be lying if he said he wasn't starting to feel the weight of expectations already starting to bend his shoulders.

"There are a lot of people who want another Gnarls Barkley album, and so do we," he said. "But we're going to do it the same way we did before — we're going to do it at our pace and see what happens. But when we get into the groove with things, we do the songs in bunches. And so we know that all we need to do is go back and start working. And if we love what's coming out, then we'll do another record; if we don't love it the way we loved this one, well, then we won't do it."

In the meantime, Mouse will keep busy with a project he's been working on for more than a year with Sparklehorse mastermind Mark Linkous ("We're not sure if it's going to be called Dangerhorse or Sparklemouse," he laughed), while Cee-Lo will work on getting Happy Hour released, plus he's got a brand-new record by the Goodie Mob to concentrate on and an upcoming greatest-hits record to promote.

So while they're both looking to the future, it's pretty much business as usual for the guys in Gnarls, and their business is, well, keeping busy.

"I'm always working on a lot of things at the same time, and Cee-Lo is too. That's the way we always have been. So nothing's ever been put on hold," Mouse said. "We worked on this record for three years, and nothing I did — Gorillaz, nothing — stopped it. And we thought it took a long time, but it ended up coming out at the right time. And hopefully that's what will happen with the second one."