What is peoples opinion on this lens? I have been looking at it and it looks like a really nice lens, and a decent alternative to the Canon EF-S 17-55... I've got a trip I'm going on in mid July and I want to get a good walk around lens, and one I can use at my cousin's wedding (the reason for the trip...Not shooting the wedding, just there as a guest and want to take pictures.) I would really go for the Canon if I had the time to save up for it, but the extra $500 I cant come up with in time. Are they comparable in IQ and performance? All the camera stores in my area carry the EF-S lens but would have to order the Sigma, so I haven't had a chance to check it out in person. I'm shooting with a 7D currently.