[minus1]

I believe there is a clear legal difference here.

These things are over the line (and illegal):

  Using images without permission

  Using code without permission

  Referencing images and code from another site without permission

Gray area:

  Designing a site from scratch to roughly copy another site's design

[jphackworth]

Referencing images and code from another site without permission

This is not illegal, merely poor form and also a bad technical decision because the other site can then control you.

If this were illegal, you would have to get permission from other sites to use iframes. Things like stumbleupon's web version couldn't exist.