The spell Floating Disk carries 100 lb per caster level, and floats 3 ft above the ground. There are specific circumstances in the spell listing that cause it to wink out of existence, but over-burdening the disk is not one of them. If you put something too heavy on top of the disk, is the disk just weighted down to the floor? Or does the heavy item fall through to the ground?
I had an idea for my first-level magus to knock a heavy opponent over onto the disk, causing them to fall through and allowing their lightweight MacGuffin to get caught on the disk. In hindsight I figure it probably doesn't work that way, but I couldn't find any rulings one way or another.
