I'm running Boston again this year and just received an email that included the following:
BAGGAGE POLICY, GEAR CHECK, AND BUS LOADING FOR OFFICIAL PARTICIPANTS
The B.A.A. asks official participants to comply with a new policy for 2014. No bags will be allowed on buses from Boston to Hopkinton, and bags will not be transported from Hopkinton back to Boston. Bags will not be allowed in certain areas at or near the start in Hopkinton, at or near the finish in Boston, or along the course. At the conclusion of the race and new for 2014, the B.A.A. will provide you with a Heatsheet® Warmth Retention Cape for warmth.
A gear check opportunity on Boston Common will be available on the morning of the Boston Marathon, allowing official participants to have a change of clothing (shoes, pants, shirt, jacket) at the conclusion of the race. The bag to be used for this purpose will be provided at Number Pick-up by the B.A.A. Only this B.A.A.-provided,clear, plastic bag can be used for this purpose. No other bags will be accepted. Any items that you would like to have with you at the conclusion of the race must be placed inside the clear, plastic bag that the B.A.A. will provide for you. You must leave this clear, plastic bag at the gear check area on Boston Common prior to boarding the B.A.A. shuttle bus to the start in Hopkinton. Please be aware that the gear check area on Boston Common is approximately one half mile from the exit of the finish area at Arlington Street.
Additional layers of clothing may be worn on B.A.A. shuttle buses and in Hopkinton for warmth before the race. Clothing that will not be worn during the race must be discarded in Hopkinton and will be donated to a local charitable organization.