I don't want a website to dictate how I experience their site. I am a guest on your site. I don't need to come back to your page when I hit the back button. That's why I hit the back button in the first place. You don't have the information I am looking for.
In a similar vein, I don't like to see other right click functions like "view page source" disabled. I don't need to steal your HTML code, but if I want to, disabling right click will not stop me. I might want to see how you achieved a certain formatting effect. If I am impressed, you can bet I'll be back.
Pet peeves take many forms online. No list like this is complete, but any webmaster that can avoid these 10 major annoyances is a hero in my book.
I look forward to visiting your site and NOT being annoyed...