Yes. Hisses even:
http://www.youtube.com/watch?v=AxyBxbGF-Qg
That's Roberto Alagna getting booed in Aida at La Scala in Milan in 2006. La Scala has a reputation for this sort of thing.
Boos were also heard (directed at, well, the director) at the premiere of Luc Bondy's new production of Tosca at New York's Metropolitan Opera just a few weeks ago. http://artsbeat.blogs.nytimes.com/2009/09/22/the-boos-for-to...