I really like the Sigma, gives consistantly nice sharp pics. If you want to see some sample shots with this lens have a look at my
gallery all the bike pics were taken with it.
I bought it after reading a review on the net somewhere comparing it to the Canon 70-200 F2.8L, I personally could not tell the difference between the shots so felt the extra money was not really worth it.
Works out pretty cheap as well I got mine off ebay from HK, all in it was £450