Yahoo has confirmed it will finally enable encryption by default for its web-based email starting on 8 January 2014.
Google offered SSL as an option for webmail in July 2008 and made it the default setting in January 2010.
Microsoft followed, offering HTTPS as an option for Hotmail in November 2010 and switching to default during Hotmail's rebranding to Outlook.com in July 2012.
UPDATE: Interestingly, after we wrote about the upgrade to HTTPS, Yahoo contacted us to gush about the fact that they'll be upgrading their RSA keys to 2048 bits at the same time, as 'an extra layer of security.
Anyway, the US National Institute for Standards and Technology (NIST), a body that you'd probably expect Yahoo to take notice of, already pretty much mandates that you should switch to 2048-bit RSA keys by the end of 2013, as part of staying one step ahead of cryptographic cracking.