I like the Yaris and would probably get one if I didn't already have the Focus, but the chassis is merely small, it was never intended to be a sporty compact which you can tell by the suspension design amongst other things. Even though its lightweight, boasting 150hp in 2007 really isn't going to knock anyones socks off either.
Its a good car, but I'd get it and use it more along the lines of what its optimized for... cheap to buy, cheap to own, and super fuel economy. The rear trunk is small, but thats why you pull the rear seats for extra weight savings and install a light flat carpeted floor!

Then its a two-door two-seater with a HUUUUUUGE trunk.