bitcoin transaction stuck in limbo
MultiBit developer here. If you're using the latest version of MultiBit HD (0.2.0 at the time of writing) then your default would have been set to a reasonable level for the current network conditions of near full blocks. You can always set it higher if needed.

If your version is older and you haven't upgraded then the default fee will likely be too low to be accepted by a miner in the current conditions. It is likely to hang around until it is finally purged by all nodes from their mempools. This can take several days.

More information is here: https://bitcoin.stackexchange.com/a/9737/117 (as suggested by @StephenM347).