Once the retweet feature is launched, some statuses flowing through all /1/statuses resources in the Streaming API will be annotated as retweets. Clients using reasonable JSON and XML parsers shouldn't require a change. Clients using brittle parsers, or those not projecting result fields, but instead using some sort of all field parsing, may wish to test their stack with synthetic retweets. The new fields are described here: http://apiwiki.twitter.com/Twitter-REST-API-Method:-statuses-retweet.
Follow the usual sources for announcements on the actual date of retweet general availability. I'd expect the launch date to be a few weeks or so away. We're taking precautions to prevent retweets from leaking into the Streaming API in advance of this full launch, but the prudent mariner prepares for the unexpected. -John Kalucki http://twitter.com/jkalucki Services, Twitter Inc.