Back in 2007, IP Innovation filed a lawsuit against Red Hat and Novell. IP Innovation is a subsidiary of Acacia Technologies. You may have heard of them -- they're reported to be the most litigious patent troll in the USA, meaning they produce nothing of value other than money from those whom they sue (or threaten to sue) over patent issues. They're alleging infringement of patents on a user interface that has multiple workspaces. Hard to say just what they mean (which is often a problem in software patents), but it sounds a lot like functionality that pretty much all programmers and consumers use.