Update: This promotional is a US only event.
On April 1, Xbox 360 owners with Xbox Live Silver subscriptions will be given 72 hours of life as an Xbox Live Gold subscriber, according to Xbox.com. Microsoft has not unveiled any other details as of yet.
Currently, gamers with a free Silver subscription have access to only
some online features, such as the ability to download games, trailers,
and demos from the Xbox Live Marketplace. The Gold membership, which
costs $7.99 per month or $49.99 for a year, includes all the benefits
of a Silver membership, plus the ability to play games online.
News source: GameSpot