I totaled my 2009 Civic Si Sedan, I was T-Boned by a full-size SUV doing 40+ MPH, the Civic Si held up superbly, so I knew I wanted another one.
So now I have had my 2012 Civic Si Sedan for a bit and can comment on it over the 09. It's a big step up, not only in looks, but in power, the torque is very noticeable and the ride is smoother. Not as sporty as the 09 but grippier than a regular civic, my Wife enjoys the ride more and its more comfortable on the road.
The upholstery... the '09 has softer plush-ier fabric, but I actually prefer the new fabric due to pet hair and it seems easier to clean as well. I miss the higher redline of the 09, but the '12 feels less of a "chore" to drive.
Favorite things would be the Torque, the iMID display is great and the Bluetooth is long over-due! I love that I can get in my car and my iPhone will just play while in my pocket, bag or trunk!
I also no longer need to install an expensive XM unit when I can now stream the app and not have to deal with signal issues from rain.
The handsfree kit is also nice and everyone I talk to says its very loud and clear.
One last thing, thank you Honda for moving the Parking Break, the old design was killing me...
Go back to the sliding armrest form the older Si, the new one stinks and seems like you have 1/2 the space now.
Also I'd like to see more technology options on the Si, Backup Cam and Warnings, Auto Wipers, Digital Rearview with Compass and Garage Opener, things like this, but overall the current tech is a nice improvement over the last mode.