....I personally own one and believe that it's a good lens but there's no way to compare to L glasses. Of course the comparison is not fair. It's like a race between Ferrari & Lada cars
I compared this lens with my 17-40L and the 18-55 IS is much sharper in the corners and about the same in the center. I also compared it with my 24-105L and got the same result. The main difference between the 18-55 IS and their L counterparts is that the L's are faster, have USM, better build. But the L's also weigh quite a bit more. Optically, the 18-55 IS is actually a very good lens.