Here's something that's more than a just a bit annoying. Have you ever quickly shot the mouse up to the upper left-hand corner of the browser window in Safari to hit the back button, only to have clicked the "close window" button instead? I've been making a habit of this lately. And it's awful.
There's just not enough space between the back/forward buttons, and the close/minimize/maximize buttons in the interface. You'll notice that the back button (an oft used task) sits just a few pixels below the close button. Clicking the close button unintentionally when you have several tabs set up with whatever you're working on will ensure certain anger, swearing and regret. Whenever I click it, for a split second I wish for an "undo" keystroke to cancel my missed mouse target. Sadly, all my current sites disappear and I'm back to square one.
Naturally, you may suggest that I use a different browser -- and indeed Firefox has a larger target for the back button, reinforced by a further separation of the browser's controls from the window options. And I've also heard there are ways to strip Safari of it's "chrome", perhaps changing the spacing between the buttons. But I'm just here to complain about the initial design choice that Apple chose to make.