Here's what happens to me today:
1) Go to page full of links. Open two of them in separate tabs.
2) Click on first tab.
3) Read page in first tab.
4) Click on link to newspaper story from first tab.
5) Before newspaper story loads, click on second tab.
6) Read headline in second tab and realize you don't want to read the whole thing.
7) Hit command-W to close tab.
That all works fine, except that I didn't know about step 6a)
6a) Newspaper story loads in first tab, and demands focus, so first tab magically comes to the front.
Which means, of course, that my command-W ended up closing the first tab and not the second one.
Argh. Whoever invented the thing that allows web pages to say "me! I'm supposed to be the top window! me! me!" should be forced to program nothing but embedded processors for thermostats the rest of his/her life. The "blink" tag had nothing on this.