The username of the currently logged in user can easily be placed in the top panel by using either:
- A purely command line method
- A gui method
1. Command line method:
Open a Terminal window with the key combination Ctrl+Alt+T and run the following command:
gsettings set com.canonical.indicator.session show-real-name-on-panel true
Below is a screenshot to demonstrate the successful result:

And this can be easily be subsequently reversed by running the following command in a Terminal window:
gsettings set com.canonical.indicator.session show-real-name-on-panel false
Easy enough to do but some will always prefer a gui solution:
2. Gui method:
If you prefer to accomplish this from a gui install the unity-tweak-tool
as follows:
sudo apt-get install unity-tweak-tool
The required setting can be found by opening the Tweak Tool and then following this path:
Unity >> Panel >> Indicators
The exact setting is illustrated in the screenshot below:

And of course the Unity Tweak Tool will allow many,many other small refinements...