Does 11.04 ship with a standard clipboard manager? If so, how do I enable it? If not, how do I install and enable one (I guess Glipper is the best best, given that Unity is running on GNOME)?
Have a look at the What Application Indicators are available?. It contains instructions on Glipper and Glippy and a few others that you might find interesting too.
To start these indicators: indicators will have an entry in the 'startup applications'. It might be set to 'off' or to 'on' depending on the indicator. If not you can add it yourself. And some you can start from dash and have a 'preferences' to set it to start on loging in.