Sent to you by Chris Hunter via Google Reader:
Everyone knows what it's like to pull two nested glasses or measuring cups out of the cabinet and find they're stuck together. Here's an easy way get the two of them apart without any risk of breaking them.
Most of us just kind of wiggle them a little until we break the seal and then slide them apart, but there's always that tense moment when you're worried you might break them. America's Test Kitchen has a better way: fill the top glass with a little ice, and then put the bottom glass into a sink or bowl of warm water. Give it a second or two to work, and the difference in temperatures between the two will cause the bottom one to expand a little and the top one to contract a little. (This is the same principle behind why running a stuck jar lid under warm water makes it easier to open.) It's not much movement, but it's enough to get the two apart safely, without much force and without worrying about breaking glass.
How to Separate Stuck Glass Cups | America's Test Kitchen