There is nothing more irritating to a visitor than a site that appears to be trying to control them, either by forcing them down particular paths, of by disabling features of their browser interface.

Here are a couple of examples of the sort of thing I am talking about:

• Opening new windows, so that the original site is still hovering in the background; if the visitor wants to come back to your site they can click the back button and if they want to open a new window they can do it themselves.
• Using scripts to disable the back button, disable right clicking, or subvert some other aspect of the browser interface.