YouAs others have said, all lenses are less sharp wide open. What do you mean "can't really be used"? Post some samples.
I have this lens and find it quite good all around. Many of my pictures from this album are wide open. Be warned, many are a bit out of focus from what would be ideal. EXIF is on the right. I also took all pictures from my one-lens challenge with this lens. The shots can be found here, though I believe most of those are not wide open.
Also, you might find Pixel-Peeper.com useful in comparing lenses (both ones you own and ones you don't own).