I'm sure it's more than a trivial amount of bandwidth, but I'd imagine it will probably become less of an issue as ISPs start caching commonly accessed information. What I wonder about is how much bandwidth is wasted in spam, junk e-mail and other online annoyances. I mean think about it; let's say Bob gets himself an e-mail address. After a year of using that address, Bob has wound up on numerous spam-bots' address lists. Bob gets a new e-mail address and begins the cycle all over again, all the while his old e-mail address is still receiving spam. Assuming a modest bandwidth consumption of 3,000 bytes per spam message and 20 spam messages per day, that's 60,000 bytes per day, per e-mail account, per person. Let's say Bob has done this 5 times (that's 300KB/day). Let's assume that one in ten people on the 'net (1/10 of one billion people) are also like Bob and we end up with over 27 terabytes of bandwidth completely wasted each day. That can be dwarfed by some other figures out there and granted, there are a lot of (realistic) estimates involved, but it's still hardly negligible.
