Why do companies produce these toolbars? I can think of two reasons:

1. as an enticement to install something they want on the client (e.g. spyware)

2. as a way to place their services closer to the user to make them more likely to be used (e.g. search)

So, to respond to your ideas:

- Useful, thoughtful plugins serve a completely different purpose

- Unnecessarily restrictive

- The problem isn't users going out and installing stupid toolbars, it's companies bundling them with other products.

I would propose this instead: since toolbar-pushers are relying on the toolbar being trivial to install and annoying to remove, the browser should just make it trivial to remove as well (a mandatory "x" on the right side that uninstalls the toolbar).