Daniel Larsson of Right Inbox sent me an e-mail to inform me about a browser extension he created that allows you to track sent e-mails and receive a notification when it has been opened. The browser extension works for Google Chrome and Firefox.
This could be a great tool for people that send out press releases, for e-mail marketers, and other professionals so that they would know whether their e-mails are simply being deleted or if they are being ignored. Some people may not like being tracked, but I can predict that every e-mail they receive from bigger e-mail chain companies like Groupon and LivingSocial have some sort of tracking mechanisms on them. Below is a demo video of how it works.