I have seen the IS-F in person but never in white, it looks very good in that color. I like white cars. Our LS and Camry are both white.
I looked at many different cars, including the ISs, when the Taste of Lexus event came to Kansas City in November. The 350 is a very high performance car and the 250 does not seem to be too far behind. I can't imagine the IS could get much quicker than the 350, but I guess they have with the IS-F. Ride is way too stiff for my tastes though. I think I will always stick with the LS.