/me climbs up onto the soap box.
As a web developer, you are assigned a certain space on my machines. I open a page, and you get the window, whatever size it may be. You can do whatever you want in your space, but leave my space and things alone. Don't resize yourself without asking. Don't touch my status bar unless it's to put a status message there. Don't go full screen without permission. And don't change my mouse.
/me gets off the box
This was one of the best things my old boss taught me when I had a web design job a few years back. And following them definitly ensures that a user dosen't get annoyed.