I disagree with the last few posts. It's easy to criticise people who want L lenses just because they are L lenses, but what this really means is that people want L lenses because they are better lenses, which is no bad thing.
tim wrote in post #2226187
Give someone like CharlesU a 300D and a 50mm F1.8 or kit lens, and take a 1DsMk2/24-70 yourself, guess who's going to take the better images?
But surely the comparison you should be making is: give the OP a consumer lens and an L lens. Guess what pictures are likely to be better.
I wanted to get the best images I could, so I replaced by 18-55 and old 75-300 with the L lenses in my sig and, although I'm not a great photographer, I have produced better images. Sure you still have to think a lot before you take the picture, but things like contrast and sharpness will almost undoubtedly be better with the L lenses.
My advice, therefore, is go for the L lenses if you can afford them. I did and I'll never look back. You don't need to be a pro.