i sold this lens
its great and better than the non L in image quality
the IS is new ,fast focus and the size is good for the bag
but it makes the bag heavy
i like the 70-200 f/4 the non IS and with IS more than this lens
It hardly makes the bag heavy - I mean compared to a kit lens, sure, but compared to lenses like the 100-400 or the 70-200 2.8's, its a feather in a bag (and handheld as well).
Actually I just picked up a Lowepro Flipside 400AW so I could have a backpack that could fit EVERYTHING camera-related I owned - not only if I decide to travel and want to bring it all with me, but also a place to store it thats better than scattered across different bags and my desk ( ) - the 70-300L is great in this bag, it takes up little space (far less than a 70-200 would) which let me have room for not only the rest of my lenses (and two bodies) but my flash and lens hoods as well (they wont fit on the lenses in the bag). Everything all fits "just" but it fits If the 85L hood wasn't as big as the lens itself is, I would have another spot open. Im going to see if I can come up with something better to store the obnoxiously large lens hoods. Only lens hood that is actually ON the lens in the bag is the 70-300L's