Today, the much talked about San Francisco startup Airbnb announced that it’s expanding into monthly rentals, meaning you can now sublet your apartment and find long-term, temporary rentals on the trendy alternative to Couchsurfing. Since its launch in 2008, there have been nearly 2 million nights booked in over 18,000 cities world-wide on its website. Even with this summer’s heartbreaking news that a girl’s apartment was vandalized after renting it out on Airbnb, the service is going strong, relying on its forgiving and open minded clientele to see the brand through.

To show its love, Airbnb is offering a pretty sweet promotion: $200 off every month for Sublets between 28 days and 6 months. My mind is already spinning with long-term travel plans. The current Airbnb offerings and its new Sublets section look nothing short of amazing.

According to Airbnb, guests have already booked over 3,000 monthly rentals, for as long as 10 months, and as high as $46,000 per reservation. So, by extending the functionality of the platform it will be able to better support the activity, draw increased awareness and expand its revenue streams. Listings will display the total monthly price directly in search results and Airbnb will accept monthly payments via credit card or PayPal.

“This is the next step in the evolution of Airbnb. By expanding our marketplace to better facilitate longer stays, we’re opening up new possibilities for the use of the marketplace by our community,” said Brian Chesky, Co-Founder and CEO. “What began with renting out air mattresses on the floor of my apartment has evolved over time to include any type of unique accommodation imaginable, now available by the night or month.”

Screen shot 2011 09 01 at 7.20.37 PM 520x51 Airbnb expands into monthly rentals and adds a sweet promotion for users

Screen shot 2011 09 01 at 7.20.44 PM 520x361 Airbnb expands into monthly rentals and adds a sweet promotion for users

Airbnb aims to redefine the multi-billion dollar sublet market by making it easier than ever to list and book properties by the month. One question does pop into mind: Considering sublets in much of New York City are disallowed by landlords and it’s a grey area in city law, how will Airbnb be seen in the eyes of legislators?

It’s likely that Airbnb will pass by unharmed. When the NYC bill to make subletting illegal was first passed, Brian Chesky responded: “This legislation is being painted as slumlords who convert apartments to illegal hotels. But as far as I can tell, this will affect thousands of families, young professionals and elderly people.”

In the end, Airbnb managed to survive unscathed and so did the likes of other vacation rental services like VRBO, Homeaway and Craigslist, the dominant players in the space, who’ve been doing this for years. Like Chesky said, the real target of the bill was: slumlords who convert apartments to illegal hotels.

There are currently over 6,000 sublets available in New York City. But a word to the wise for NYC subletters looking to make a buck on Airbnb: The real issue here will be when people choose to sublet their apartment for more than it is worth, which will have NYC landlords up in arms.