Meta Linden prepared the SL Key Metrics for July 2007. Besides some new numbers on performance and stability, the following I find interesting:
24.3% of the active SL avatars (Total: 1,038,501) are female, and they spent 42.1% of all online hours. This means female avatars spent in average 40h online a month, and males only 17h.
If you dont want to use software to view them, use the Google Docs online version.