Times have been tough for Twitter, which has seen its stock price decline fairly steadily since last spring and laid off eight percent of its employees last October. Now, the city's second-largest tech employer is subleasing a hefty quantity of office space in its two Mid-Market buildings, presumably to help bring in a little extra cash.

According to the SF Business Times, Twitter has made four spaces immediately available for sublease: one in the historic former SF Furniture Mart building at 1355 Market St., and three in the adjacent building at One 10th Street. Together, they total 183,642 square feet, enough space for 1,416 employees—making the office sublease San Francisco's largest.

The city's office availability rate rose to 11.7 percent this quarter, up from 10.8 percent last quarter, while its vacancy rate is 6.3 percent (up slightly from last quarter's 6.2 percent). But for those wondering if the tech bubble might be deflating, a researcher says that those numbers are "relatively low," and that SF's office market remains strong compared to the U.S. as a whole.

Twitter's woes may also be reflected in the fates of nearby high-end restaurants: Bon Marché (in its building), Cadence (across the street), and Oro (a few blocks away) all closed this summer after less than a year in operation.