The numbers of units being built in the linked SF Business Times article [0] seems to contradict those from the SF Chronicle [1].

Business Times:

    Nearly 8,000 new apartments, mostly in mid-rise and high-rise buildings, 
    will come on line between now and 2015 — 3,498 in 2015 alone. It’s more 
    new rental housing than was built in the last 15 years combined, according 
    to real estate research firm Polaris Pacific.

SF Chronicle:

    Largely in response to the city's growing technology sector, 22,000 residential 
    units are in various stages of approval and construction. … Since 2008, only 
    about 1,710 units were built each year, compared with an average of 2,220 each 
    year between 2004 and 2008, according to the department.

If the average was 2,200 housing units built each year between 2004 and 2008, that's 11,000 housing units. Granted the Business Times is using apartments as units, while the planning department uses housing units.

Looking at the planning department data [1], there are currently 28,010 housing units approved and 3,930 under construction. The total pipeline is 43,580 units. For the previous reports they provide, we've got:

  * Q1, 2007: 9,305 filed, 4,736 approved, 4,978 under construction, 30,002 total
  * Q3, 2007: 10,708 filed, 5,005 approved, 6,134 under construction, 31,761 total
  * Q4, 2007: 20,890 filed, 4,570 approved, 6,790 under construction, 40,370 total
  * Q1, 2008: 34,510 filed, 4,560 approved, 7,520 under construction, 53,980 total
  * Q2, 2008: 32,370 filed, 4,780 approved, 7,480 under construction, 51,470 total
  * Q2, 2009: 34,570 filed, 6,200 approved, 6,510 under construction, 54,610 total
  * Q4, 2009: 30,370 filed, 8,220 approved, 1,320 under construction, 46,600 total
  * Q2, 2010: 30,780 filed, 5,870 approved, 1,480 under construction, 43,780 total
  * Q3, 2010: 20,710 filed, 16,690 approved, 1,180 under construction, 44,100 total
  * Q1, 2011: 15,610 filed, 22,590 approved, 1,730 under construction, 45,820 total
  * Q2, 2011: 7,620 filed, 29,760 approved, 1,820 under construction, 45,760 total
  * Q3, 2011: 7,620 filed, 30,280 approved, 1,990 under construction, 46,620 total
  * Q1, 2012: 6,180 filed, 27,670 approved, 3,990 under construction, 42,520 total
  * Q2, 2012: 6,940 filed, 28,060 approved, 4,220 under construction, 43,280 total

So, data-wise, it's not clear this is as big a construction boom as it's made out to be. As an SF resident, however, I've never seen so much housing under construction, so maybe it's just more visible?

Does anybody else have any data?

[0] http://www.bizjournals.com/sanfrancisco/print-edition/2013/0...

[1] http://www.sfgate.com/bayarea/article/S-F-apartment-construc...

[2] http://www.sf-planning.org/index.aspx?page=1691