Of course, this means more work for Ged Maheux, tracking down each person and letting them know that, no, they can't use the icon, because it's for a piece of commercial software.
The good news is that there are, however, plenty of design alternatives to the Iconfactory's copyrighted artwork. Lots of friendly, smiling flyers have come out of the woodwork/birdhouse -- and they're free to use for your website or other non-commercial project. Read on for a rhapsody in bluebirds.
Function has the friendliest, smiliest alternative for you.
If you're the curious, inquisitive sort of tweeter, then this member of Smashing Magazine's Practicka icon set is for you.
If you're looking for more of a badge than an icon, Randa Clay has some good options.
Want to create your own? Vectortuts has a great tutorial.
All of these are free to use, but some have certain rights restrictions (with regard to commercial applications) or linking requirements attached. Make sure you understand what permission you have to use the artwork posted before you go and snatch it.