I came across this online game, Bloxorz at http://www.albinoblacksheep.com yesterday and have found it really good for killing a lot of time. The idea is to get the block through the hole using the arrow keys to move it. If the block rests on one of the round pads then sections of the floor disappear or reappear. There are also pads that only activate when the block rests on them while on its end and orange floor sections that collapse if the block rests on them while on its end. I have got up to stage 28 at the moment, but keep forgetting to note the passcode for the current level down so I can restart from that point.