So a few months ago, United and Marriott announced their RewardsPlus Partnernship.
The key details are, from the site:
We appreciate your loyalty to United® – and now your MileagePlus Premier® recognition and benefits just got better. Together MileagePlus® and Marriott Rewards® bring you RewardsPlus, a new program with great benefits to enhance your travels.
Premier Gold, Premier Platinum, Premier 1K® and Global ServicesSM members can now register for RewardsPlus and enjoy complimentary Marriott Rewards Gold Elite status and benefits. Also, all Premier members can convert their MileagePlus award miles into Marriott Rewards points at an exceptional rate, and all MileagePlus members can enjoy greater value when they convert Marriott Rewards points into MileagePlus miles.
Basically as a Marriott Platinum Premier member, I got my United account upgraded to Silver status. This was nice because United Silver members can choose an EconomyPlus seat within 24 hours of the flight. On a recent United Chicago to Houston this paid off for me and instead of a middle seat way in the back I had a middle seat in Economy Plus which had generous legroom.
Don’t forget to sign up at the link above if you haven’t already and enjoy the reciprocal elite benefits.