A Florida based company called Solomon Technologies was granted a patent some fifteen years ago for tech related to hybrid power-trains. I won't address whether or not this particular company can be considered a patent troll, since I haven't had a chance to read the patent in question. However, they did wait about eight years after the introduction of the Prius before filing a patent infringement suit. They filed suit against Toyota (but not Ford who has a cross-license deal with Toyota) in September 2005 and a complaint with the International Trade Commission in February 2006.
The ITC complaint sought an injunction to prevent Toyota from importing and selling hybrids in the US market. Yesterday, an administrative law judge ruled in favor of Toyota and declared that at least one of the claims in the patent was invalid. The case could steal be appealed to the full commission and also US Federal Courts. So Toyota hybrid sales in the United States are safe for the moment, but this case is likely to drag on for some time.
Thanks for the tip, Michael!