Hey guys, I'm currently having a debate with myself. I have the kit 18-55 that came with my XSi but I have been wondering for a couple weeks now whether or not the 17-55 will be of benefit as a walk-around lens? It seems like the 2.8 constant aperture plus IS will get me many more opportunities (especially while on vacation) than the kit lens. I have this tentative plan of getting the 17-55 and then the 70-200 f/4L to add to my 50 1.8. Money aside, is the 17-55 worth the upgrade over the 18-55?