Zotero is being sued by Thomson Reuters, the makers of Endnote and one of their proprietary competitors. The reason?
“A significant and highly touted feature of the new beta version of Zotero, however, is its ability to convert – in direct violation of the License Agreement – Thomson’s 3,500 plus proprietary .ens style files within the EndNote Software into free, open source, easily distributable Zotero .csl files.“
If you’re an Endnote user and wish to move your existing citations to an open and accessible format, will Thomson Reuters let you? Or will you, too, be sued for trying to access and manipulate your own data?
Just one more reason to use open formats on free/open source systems.

Follow-up: Mark Leggott has also posted about this, with the suggestion that funds for legal defense can likely be found from the hordes of Zotero-using institutions and individuals.
darcusblog also has a good comment about this lawsuit.
[...] to be a bit murky. Some bloggers say the allegation is false, and that this is a SLAP suit. Others wonder if this means anyone who migrates their citations from Endnote to something else are equally [...]
Just to clarify what is said in the second paragraph: the lawsuit appears to be over the EndNote style files — the definitions of how to format a citation in specified form — and not on converting citations themselves from EndNote to Zotero. A posting in the Zotero forums says that GMU is going to issue a statement on the lawsuit soon. I also have more commentary and links to critical bits in my blog post.