I don't think this is proprietary so I'll share it.  I'm a member and captain (B752) at Delta Virtual.  My airline keeps statistics of use.  Last month (July) 22,610 flight hours were recorded at DVA.  That consists of 8,225 legs.  Of these, 5,315 legs were flown using FS9 (64.6%) and 2,876 legs were flown with FSX (35%).  The remaining 33 legs were flown using "other" such as 2002 (0.04%).  So, 64/35 FS9 to FSX!  I think this is a good indicator of the popularity of FS9 and developers would do well to recognize these ratios!   :)