Arctic Sea Ice appears to have reached it minimum extent for the year, at 4.53 Mkm2 (IJIS data; NSIDC gives 4.33 Mkm2).
That's the second lowest in the records, after 2007's 4.25 Mkm2 (IJIS).
However, I think a more relevant metric (after volume, of course) is the extent's yearly average. By that measure, 2011 is the lowest, at 10.65 Mkm2 (as of Sept 14th), lower than 2007's 10.70 Mkm2 as of the same date that year.
Last year at this time the year-to-date average was 10.91 Mkm2. We'll see how the year ends. The 2007-2011 difference peaked at 0.062 Mkm2 on August 24th, and lately 2007 has been gaining ground to where the difference is now 0.043 Mkm2.
In terms of volume it's not even close: the latest PIOMAS data, which gives modeled ice volume up until 8/31/11, has that date's sea ice volume as 36% below 2007. (4.28 Kkm3 to 6.65 Kkm3.) That's astonishing. Over 1/3rd of the sea ice have melted in just 4 years.