First, I have to agree with Fozzy (and I was not sure that would happen in my lifetime ;D

; big hugs, right, Foz?). It is probably going to be a matter of transition over time.
That being said . . .
I am particular to FS9 right now simply because I can get better performance out of FS9 on my present computer systems than I can get out of FSX. My dad has a much better system than I do, and he prefers FSX because he can get more out of FSX than FS9 because his system can handle it. Really, if there is one big drawback to FSX, it is that the software is way ahead of what seems to be the most common hardware that people have. Once the hardware catches up to the software, then FSX will start coming into its own.
That being said (#2) . . .
FS9 had incredible developer support. While it can be time consuming to install this add-on or that, FS9 can still give the potential of FSX a good run for its money simply because of the massive amount of support it enjoys. FS9 was a truly benchmark piece of software when it comes to flight simulation for the home user. If you set aside graphics, FSX was a fine-tuning over FS9, but it didn't reinvent the wheel. So, while FSX has a lot of untapped potential yet to be discovered, FS9 is still a truly great piece of software, and having it in one's software library is definitely a good thing for any aviation/flight simulation enthusiast.
So, my grand conclusion from all my rambling is:
Murjax! Why didn't you include a poll option for BOTH?!? ;D

I am so proud of myself for agreeing with Foz,
~Darrin