The problem there is that they were already dragging it out for the sake of dragging it out before the first season even ended. There was a point when you could tell that the show's success had sunk in and the network had told them to stretch out their story arcs to fit the longer run the show was now expected to have -- because up to that point, the characters had been growing and evolving, but suddenly they just started backsliding and going into holding patterns. Sometime early in the second season, I just lost interest and stopped watching.
Just like with Smallville
. Really, once Jonathan Kent died, none of the characters really grew, especially Clark: he just seemed to stay still from early-Season 5 till the producers finally decided it was time for the cape and tights in Season 10.