Maybe it’s the new web 2.0 designs that utilize icons extensively. I don’t know but I’ve got a pretty big folder filled with all kinds of GPL icons for use in various projects. I use them in web based software but mostly in web sites and membership sites. It’s a personal preference thing. To me, icons help visitors and members quickly identify different sections of a web site. Here’s a list of sites I’ve found that regularly feature or distribute icons from.
One caveat, some icons are open source but some aren’t and have limitations on commercial use. Most of the time, using them on your own projects / sites is OK, but please make sure you check and understand the licensing of these icons before you use them.