One of the biggest mistakes I made was to buy this lens when I got the 20D. It took me nearly two years to realise that the reason my pictures on the 20D were so lacking in sparkle comapared to the 300D (Digital Rebel) was the use of this lens. It makes you realise just how good the kit lens is. This lens by comparison is not sharp and very lacklustre in terms of results. The kit lens is clear, bright and colourful.
Here's my advice: DON'T!