If you're one of the many players who is having issues with the Headless Horseman pumpkin locking up your game client or any other cogwheel type item doing the same sort of thing, there is now a workaround while they look into fixing this bug. Kill your tooltips.
That's right, tooltips are the cause behind this rash of client crashes. There are two ways you can get around this particular issue. One is to just disable tooltips. You can do this by setting up a single macro and putting it on your action bars.
This will disable tooltips when you left-click the button and re-enable them when you right-click the button.
An alternative is a simple addon called CogFix which disables the simple addons which are causing this issue, but will allow complex tooltips (like when you mouse over a player or NPC) still remain visible. Any custom tooltip addon could possibly protect you from this bug, but your mileage may vary.
The developers are working on permanent a fix for this issue, but have to test things to make sure that the fix doesn't cause issues elsewhere.