Visto filed a patent infringement case two weeks ago against Microsoft and their misuse of some email sync technology that Visto says they own the patent on. The suit seems to focus heavily on ActiveSync and Windows Mobile 5.
From the press releases it seems that Visto spends a lot to time in court so they must be pretty confident with the case against Microsoft.
http://www.visto.com/news/releases/05_12_15_microsoft.html
- Joel