I would like to learn how others come down on this issue. I recently ran up against what I consider to be a practice which may be illegal on the part of McAffee Associates. They have intentionally designed their internet protection suite, including versions widely distributed by commercial network service providers like Comcast to force users to install their product on all the machines on the peer-to-peer network supported by Microsoft networking software. Their programs are designed to force the use of their product. Their documentation is fairly up front about it. They basically say, if you want to share on a network, all the clients who are sharing must be running an agent contained in their software. Over the last couple of years, there have been some pretty annoying bugs in that agent component.
For me, as a consultant with portables and clients with many different security packages, this practice is a PITA. It means that either I must frequently install or reinstall security software as I move from one network to another, or run several different packages on the same machine, constantly wasting a lot of resources and inviting problems, or do without certain sharable devices connected to systems that for one reason or another are not running their dumb product!