It's not that big of a deal, but it's still pretty annoying. I let it go when it's a one-time accident. If the same person keeps doing it, acciental or not, I'll give them a look or say something about paying attention or knocking it off.
16 Capita BSOD . 16 NS West . 15 NS Snowtrooper BIA . 13 Salomon Pow Snake
15 Now Drive . 14 Burton Genesis
14 Flow Hylite