###Updated to include the last two quarters of 2012.
I think what's most interesting about the update is how the numbers have changed over time. For instance, when I originally answered this question quarter 1, 2012, was complete. There were 409,490 undeleted, open, questions that quarter of which 85.61% were answered and 70.71% answered "well". Those numbers today are 405,131 questions, 87.47% answered and 74.30% answered "well", which implies that as time goes by the Stack Overflow community is doing something about the older answered questions, just not very much. The increase in the number of questions with a score of 1 or more also indicates that SO users are upvoting (viewing/using?) older questions, which is good.
The extremely noticeable consistency between the current and previous results is the fact that all these downward trends have continued, things are getting worse. On current trends, quarter 3 2013 will have less than 50% of questions where an answer is either upvoted or accepted. If the trend in answering/deleting older questions continues then it'll be rescued later but the same will happen again, permanently, around quarter 1 2014.
This is a "problem" that needs to be fixed, somehow.
Year Quarter Questions Answered GoodAnswer
---- ------- --------- -------- ----------
2008 3 1814217508 99.98%99% 99.78%83%
2008 4 3955738790 99.85%87% 9798.89%11%
2009 1 5428653441 99.71%73% 9596.96%23%
2009 2 7613375339 99.51%56% 9394.85%24%
2009 3 9929198426 99.18%22% 9192.91%49%
2009 4 114135113136 9899.97%02% 91.02%72%
2010 1 144028142909 98.56%62% 8990.97%76%
2010 2 160493159213 9798.91%01% 8788.36%50%
2010 3 188612187222 97.41%56% 8687.03%32%
2010 4 207395205903 97.23%41% 8586.47%87%
2011 1 269672267895 96.71%98% 8485.21%83%
2011 2 301200298140 9596.34%16% 8284.10%30%
2011 3 335106312239 8895.66%30% 7582.21%52%
2011 4 339592316593 8794.62%46% 7381.92%55%
2012 1 409490405131 8587.61%47% 7074.71%30%
2012 2 419391431420 8185.33%41% 6471.74%38%
2012 3 452507 83.44% 68.07%
2012 4 461118 80.62% 64.02%
Year Quarter Questions Answered GoodAnswer
---- ------- --------- -------- ----------
2008 3 1808417454 99.98%99% 99.78%84%
2008 4 3937438618 99.85%87% 9798.91%13%
2009 1 5393053133 99.71%73% 9596.98%24%
2009 2 7556574795 99.51%55% 9394.86%26%
2009 3 9841197569 99.18%22% 9192.94%52%
2009 4 112677111776 9899.96%01% 91.06%77%
2010 1 142475141491 98.54%60% 90.03%82%
2010 2 158929157757 9798.90%00% 8788.39%54%
2010 3 186719185404 97.38%54% 8687.04%34%
2010 4 205092203733 97.20%38% 8586.52%91%
2011 1 266760265103 96.68%95% 8485.26%88%
2011 2 296514293660 9596.27%11% 8284.13%35%
2011 3 327715305355 8895.40%20% 7582.11%55%
2011 4 330472308130 8794.28%31% 7381.74%54%
2012 1 395629392376 8587.10%07% 7074.48%14%
2012 2 402573417341 8184.11%92% 6471.78%18%
2012 3 436875 82.85% 67.81%
2012 4 443642 80.31% 64.00%
Year Quarter Questions Answered GoodAnswer
---- ------- --------- -------- ----------
2008 3 1631215797 99.98%99% 99.83%88%
2008 4 3330432945 99.88%90% 98.81%87%
2009 1 4150641381 99.76%74% 98.12%18%
2009 2 5331653922 99.70%63% 97.33%38%
2009 3 6449165645 99.53% 96.49%71%
2009 4 6787569626 99.30%35% 95.56%97%
2010 1 9774399493 9899.97%02% 94.19%66%
2010 2 101814104134 98.41%50% 9293.33%04%
2010 3 113190116514 9798.94%10% 9192.29%16%
2010 4 118231122588 9798.81%00% 9091.87%82%
2011 1 146083152765 97.48%79% 9091.11%31%
2011 2 161480169152 96.51%96% 8889.55%90%
2011 3 158318167683 95.30%92% 8688.54%18%
2011 4 154275165138 94.38%92% 8586.07%80%
2012 1 166750183482 93.16%92% 8385.35%34%
2012 2 150147180243 92.93% 83.66%
2012 3 173618 91.25%26% 80.49%88%
2012 4 188466 87.52% 74.33%
Year Quarter Questioning Answering
---- ------- ----------- ---------
2008 3 64516411 90919007
2008 4 1075510724 1336613276
2009 1 1373913713 1608515995
2009 2 1896618929 2135121276
2009 3 2451124474 2577425631
2009 4 3747937388 3666036124
2010 1 4756447454 4219941411
2010 2 5707256895 4783846868
2010 3 6654666340 5352452398
2010 4 7340473162 6109059578
2011 1 9567095347 7631574931
2011 2 109801108828 7970278798
2011 3 127506118150 8646185501
2011 4 125765117156 9096089839
2012 1 152582151337 109684107792
2012 2 164801167394 114608116139
2012 3 182767 125379
2012 4 201461 133558
