Texas Senator Kay Bailey Hutchison has announced that she will keep her Senate seat while running for Governor of Texas. She had previously indicated she would resign the seat to allow for a special election.
Officially she is doing so because she wants to remain in Washington to participate in the ongoing debates over health care, financial issues, global warming, etc. This is not an implausable explanation since her resignation would leave the GOP short a seat for a period of time.
However some speculate it could also be a backup in case she loses the primary she would still have her seat. A rcent poll showed her trailing Rick Perry by 11 points.