The most high-profile case is Enercon[1], but in general it is a problem that most companies won't admit to it publically (even though everybody, all of a sudden, is talking about it now). Maybe most telling is that the German government wanted the US to sign an agreement which would have prohibited industrial espionage of the US against Germany. The US refused to do that[2].

[1] http://en.wikipedia.org/wiki/Enercon#Patent_dispute [2] http://www.spiegel.de/spiegel/print/d-120780529.html