Flickr And Yahoo Mail
Those two need obvious work and are relatively easy to do.
Can Marissa Mayer turn Yahoo around?
Make it free again. There should be no limit to how many pictures you can upload.
Give the option to embed. I should be able to embed a Flickr picture - not just mine, but of anyone who will allow it - into a blog post of mine.
There is a need for cloud storage, like Dropbox, Skydrive, Google Drive. So all email attachments go to the cloud. Inboxes don't have space limits these days.
Yahoo Mail spam protection sucks. I can block email from an email address, and the next time I get an email from that address, it still gets delivered! Fix this.
Tap into them. Facebook has one. Twitter has one. LinkedIn has one. Google Plus has one.
Overlap these graphs onto my Flickr and Yahoo Mail.
Go mobile on both.