I can recommend [StackEye][1], a Chrome extension that allows one to follow SE users (as well as particular questions). It adds a Follow button to each user's profile: 

![t.b.][2]

The notifications on the extension icon are an unobtrusive number (not some flashy-red thing). Upon a click, you get a list like this: 

![enter image description here][3]

Although not see on the screenshot, questions asked by followed users are also included in notifications. 


  [1]: https://stackapps.com/questions/4454/stackeye-chrome-extension-to-follow-users-and-questions-on-stackexchange-sites
  [2]: https://i.sstatic.net/Pu6Ro.png
  [3]: https://i.sstatic.net/4pjS7.png