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Ms. Robinson’s business, which opened in April, caters to young professionals and offers walk-in, 30-minute massages.

Consumers seem equally happy with the service.

Courtney Knapp of Petworth, for example, says she has signed up for at least five deals so far - everything from Pilates lessons to dog grooming services.

“It comes out to about one a week,” she says. “I’ve been really impressed with it so far.”

Aside from the good deals, she says, the site is helpful in highlighting new businesses to residents and visitors.

“I just found out about a restaurant in Petworth, where I live, through Groupon,” she says.

The restaurant: Brightwood Bistro. The offer: A $15 gift certificate with a value of $35.

“I love the collective-bargaining-power idea; it’s a great business model,” she says. “And I love the nerd power of it.”

Any downsides to it?

“I could run out of money,” she says half jokingly.

Mr. Mason attributes some of the site’s success to the recession.

“I think one of the reasons for our success is that people got used to certain luxuries” during better economic times, he says. “What Groupon does is allow people to do those things.”

Such as stay at the Hyatt in downtown Chicago for $99 a night — a recent featured deal. Or get teeth-whitening for $185 (value $600) — a recent D.C. offer.

“It’s amazing. We kind of did this on a whim,” Mr. Mason says. “We had no idea it was going to take off like this. Now we’re just trying to hold onto the reins.”