Recently I turned 20K on my 2007 Fit so let me give you my opinion.
I was considering both the Fit and SX4 a while back and finally went with the Honda. It gets much better MPG (37-38 with the five speed in mixed driving), has more after market parts available and has won just about every automotive award and comparo that it's been featured in. I liked the ride and handling in the Fit much more than the SX4. The magic folding rear seats are extremely useful and let you carry a wide variety of large items with no problems. Resale is fantastic too. A lot of people say that it doesn't matter what the car is worth if you plan to keep it but if the car gets damaged or totalled then resale value determines your settlement.
The only hitch I can see is that if you want a Fit you are going to pay sticker price and probably wait for the color, package and transmission of your choice. I had a three month wait for mine back in early 2007. You can buy an SX4 right from the dealers lot at a discount off of sticker in my area.
The only things I don't like about the Fit are the quality of the carpeting and the gearing of the transmission. I'd prefer it to be geared a bit better for mileage or the addition of a sixth speed.
If you can hold off your decision for a while you may want to wait for the new Fit to come out this fall. From what I've seen, it's a bit bigger and has a few extra horsepower, is better looking (IMO), and gets even better mileage.