I have a central vac system and I loveitloveitloveit. All the dust, dirt, hairballs, random Lego toys and crumbs whisk away through the tubes into the canister in my basement. Every few months I empty the canister into the field by the compost pile, pick out the random toys and restart the process.
Until my children decided to roll their Magnetix balls into the second floor inlet. The heavy metal balls rolled until they reached the first bend in the tubes and then they clustered there. All twenty of 'em. In one heavy, magnetized mass that no amount of suction could budge. They blocked all suction in the pipes and I couldn't clean my floors.
One service call, one section of tube cut out and replaced, $110.24 spent, one heated lecture about using the vacuum cleaner inlets as a toy ('cuz it's MOMMY'S toy), and a man-sized fistful of metal balls thrown in the garbage later, we've concluded that magnets are powerful.
I put the receipt in Mr. G's baby book because I'm pretty certain he was the sinister mastermind of this particular plan.