Twitter Starts A Users' Weekly Digest On eMail [blog.twitter.com]

Starting today, you can discover the best of Twitter in a weekly email digest delivered to your inbox. This summary features the most relevant Tweets and stories shared by the people you’re connected to on Twitter.

We’re rolling out this new email out to everyone over the next few weeks, so keep checking your inbox for new messages from Twitter.

That may help give tweets a longer life. I could also imagine they'd have room for sponsored sections, too.