Someone on one of the forums requested a form multiple select element which would only allow a few selections. It sounded like a challenge and a couple days later, I finally figured it out! The form element doesn't completely mimic how a normal multiple select would work (for example, the control key resets the list and just clicking on the entries adds to the list) - but a minor variation to get the desired result. It adds the entries and tracks the order the entires were selected (so the oldest is dropped off when a new one is selected)

Limit MultiSelect Example

Check it out!