Supposedly Prosper got a really good deal on the office lease by taking over the space from some failed dot com or something.

Who knows .. if they could legally sublet the space to take something cheaper. And I believe that the commercial real estate market isn't so hot anyway
Good point about the practical difficulties of reducing costs at this point.
The 10Q says
Prosper leases its corporate office and co-location facility under noncancelable operating leases that expire in July 2011 and August 2011, respectively. Prosper’s corporate office lease has the option to renew for an additional three years. Future minimum rental payments under these leases as of September 30, 2009 are as follows:
Remaining three months ending December 31, 2009 $107,012
Years ending December 31:
2010 431,864
2011 265,513
Total future operating lease obligations $804,389
Rental expense under premises-operating lease arrangements was approximately $106,248 and $315,690 for the three and nine months ended September 30, 2009, and $94,748 and $272,309 for the corresponding periods during 2008.
The 2011 number above is for a partial year. The 2010 number is a full year, so we can use it to compute. $431,864/12 = $36,000/month. The colo cost has got to be a small fraction of this, so I believe it is mostly office space. According to
http://111sutter.com/index.cfm?NOaction=propProfile its a 286,182 sq ft building. Its 22 floors, so if we divide 286182/22 = 13,000 sq ft per floor. $36,000 / 13,000 sq ft =
$2.76 / sq ft. Doesn't sound like a deal. Doesn't seem like frugal startup office space to me.
The building has vacancies, listed on
http://111sutter.com/index.cfm?NOaction=leaseInfo Entire 4th & 19th floor empty now. Entire 12th, 13th, 14th, 16th goes vacant April 2010.