Microsoft and Open Text fired a shot across Interwoven's bow yesterday when they announced a partnership that has Open Text offering a SharePoint based Matter Life Cycle Management solution. Open Text's Enterprise Search expertise, clearly brings a lot to the table here.
Interwoven countered with an announcement they had partnered with Vivisimo, OEMing their clustering technology to deliver a product called Universal Search to professional services firms.
Enterprise Search is core business for Legal Firms. I suspect we'll be seeing many more announcements of this sort in the coming months.