A new feature has been added to Gmail, allowing users to now add a calendar event directly to their Google calendar. While it's at it, Gmail will also assign a name to the event, though you're free to change the name. The update will be gradually rolling out to US English users, though other languages are also in the pipeline. For those who have received the update, dates and times within emails will now be underlined, and users can click on them to preview the date, time as well as event name before adding them to their Google calendar without needing to leave Gmail.
Source: Gmail Blog