There is some controversy about whether or not this effect actually exists. Despite the issues with adequate subject controls, this idea is applied widely to corporate fiefdoms, artist's work, and other areas.
It's tempting to think that we think of our own items as having a higher worth than those of others, but it might not be the case.
Endowment Effect at Wikipedia for more examples.
The Willingness to Pay/Willingness to Accept Gap, the Endowment Effect, Subject Misconceptions and Experimental Procedures for Eliciting Valuations for a discussion of how maleable the endowment effect can be.
Valuing Attribution and Publication in Intellectual Property for a somewhat related study of how artits value their work.