OH OH OH ... I got a good one.
When you are planning on going out somewhere, jump in the car, fire up the GPS..
"You have 3 updates (0.9GB) to install:
Software Update - 600MB - Required
Map Update - 300MB - Optional
Speed Camera Update - 500KB - Optional"
So you start installing them, and think "okay lets start driving", only to have the GPS 3 turns up the road shit its pants "The update you are trying to install needs to download, please reconnect to Wifi".
*press OK*
"Your GPS has no maps installed".
Me: "Fucks sake".
30 minutes later it finishes downloading and updating/installing, resulting in us being way later out the door than expected.