Launching just 12 weeks ago, Fab.com is already upping the ante with new ”Online Pop-Up Shops,” giving the popular retail pop-up shops in the real world a digital runaround.  The flash sales site’s membership has quickly grown to more than 600,000 members, who have placed more than 80,000 orders of more than 160,000 products from more than 500 design partners who have teamed up with us to rapidly make Fab.com the single-largest online marketplace for design.  Site visits grew from 1.8 million in July to 2.5 million in August, and September is tracking to be even bigger.

For its first online pop-up shop, Fab is featuring “Fast Company Magazine Presents U.S. Design,” showcasing American-made products from 76 top U.S. designers to coincide with Fast Company’s current issue. The pop up shop will stay up for 30 days on Fab.com and will offer discounted items exclusively for Fab members. As an added bonus, Fast Company is throwing in a free subscription to its magazine with every purchase from the Pop-Up Shop.

Fab.com launches today with 200,000 pre-registered members and over 175 designers and manufacturers.  Flash sales will launch daily at 11 AM Eastern Time, 7 days per week and lasting for 72 hours. As is common with flash sales sites, upcoming deals are announced exclusively to members, through the Fab.com website as well as daily e-newsletters.  Fab.com membership is free, but the startup says numbers are restricted in order to maintain “exceptional prices” for design products in a range of categories including furniture, home accessories, technology, lighting, art and toys, to name a few.

The space is certainly booming, and extending into niche areas with new marketing tactics for each audience.  Amazon’s flash sales site MYHABIT announced the first in a series of curated and vintage sale events, offering customers access to exciting collections at a broad range of price points. “The Curator” series of events will include hand-picked items from the industry’s top tastemakers. “Archive” events will feature vintage luxury and designer clothing, jewelry and accessories.

“Every woman should incorporate glamour and vintage into her wardrobe to develop her own unique style,” said Janie Bryant. “My curation represents a fusion of some past and present fashions that I love and I’m excited to share it with MYHABIT customers.”

Moreover, Gilt Groupe‘s luxury travel arm Jetsetter has been providing high-end hotel and resort bookings using the flash sales method since 2009.  Now in 2011, Gilt introduces vacation home rentals, Jetset Homes allows high-end travelers to sift through an array of 200 beautiful luxury homes.  The rentals are a tad expensive. The 14-bedroom island mansion is up for grabs at Jetsetter’s vacation home rentals section.  Members can book the property for a discounted rate of $54,000 a night.

Jetsetter will add its own twist by picking five to ten homes to feature each week and mark down by 20 to 50 percent off.  To start, it will have an inventory of more than 200 homes, which will be available in locations such as the Caribbean, Mexico, California, France and Italy.

“Developments from companies like Jetsetter are positive for the vacation rental industry, which, before HomeAway entered the scene, was a fragmented industry with no single source that consumers could turn to when looking for an alternative to traditional hotels,” says Eileen Buesing, a HomeAway representative.