Gravity pulls ink down. If you store your markers in a cup like I do you'll always get squeaky markers that perpetually run out. A better way to store them is perhaps upside down, like new ketchup bottles, they working with gravity.
The problem then becomes that it's harder to tell the colors apart.
A simple packaging re-design would probably encourage markers to be stored up-side down and whiteboards the world over would rejoice.
On a semi-related topic we released an update to our Whiteboard iPhone/iPad App.