This is my first post to the forum, I am shopping for an IS-F and trying to decide if the pre-2011 models are worth considering. I currently drive a Mazdaspeed 3, so probably wouldn't notice what Lexus owners would consider a "harsh" suspension, the Speed 3 is an infamous go-cart in terms of ride.
I'm not crazy about the fake exhaust pipes but could live with them...is there anything else about the pre-2011 models, a real dealbreaker, that I should consider?

There are a few cosmetic changes but the big differences are the ride, the diff (I believe it came in the 2010's as well) and the instrumentation. All the rest is the same. The ride is the biggie. I have an 08 and love it but I am also looking for a reasonable 2011. As for fake exhaust tips, lots of high end cars do the same so that shouldnt be an issue.
Good luck.
Andy

Tips aren't fake. They are functional diffusers for each muffler outlet.

My 2010 ISF has adaptive headlights, they are great if you like the twisty bits at night.
I believe Lexus discontinued the feature in 2011. You will become addicted the first time you drive a 400+ HP 8-speed paddle shifter, I also have a RX-8... I gave it to my daughter... The ISF is a truly world-class sedan. But remember that performance costs... But once you get service at a Lexus dealer you will never go back to a Mazda dealership... Also keep in mind that if you are a modifier, good parts are hard to find and are serious $$$... But you can keep up with just about anything on the autocross track if you know how to drive.
Gas on!
Pete in Aptos, CA

LOL Interesting way to put it

There are a couple of exhausts that do away with the tips. As much as I disliked the tips before owning the car, once I realized they serve a purpose and I saw them every day I came to like them.

The main things to consider between the years are the newer instrumentation (old: equal sized tach+speedo, new: big tach centered), the LED headlight strips (which does away with the headlight turning feature), and the suspension tweaks in more recent years.

Coming from a MS3 you will enjoy any year ISF. With my background in Mitsu/Subarus with coilovers, I don't find the 08 ISF to be as harsh as people claim. It's certainly not an idea setup but you shouldn't have any complaints. And I got a steal for my 08 so there are some nice deals out there.

I'm wondering if the softer ride in the post-11 models comes at a price. The harsh ride in my Mazdaspeed translates into insane cornering ability, and I wonder if the older, harsher IS-F's corner better than the new ones.
Edit: I found this article, which destroys my theory about older IS-F's cornering better:

It would hobbyhorse down uneven pavement and batter occupants in a straight line but roll excessively in corners. For 2011, Lexus addressed these concerns in a big way, changing or retuning every major suspension component. Sorry, as a new member I can't post links yet...it's from a Car and Drive review.

In '10 or '11 the ISF received a Torsen limited-slip diff that makes a huge difference in handling. So look for a newer model if you're big on handling. There are times when I can definitely tell I don't have one but honestly, it's mostly when turning sharp up an angled slope into a parking lot more than anything.

Same boat as the OP.

Best thing to do is test drive both years. I test drove the 2011 and it is different than the 2008 ride wise.

Testing 2010 shortly to see what's what. There price difference between them right now is about $7000 +/- $1500.

I've decided to go with a post-2011 model. I'll post pictures when I get it.