When the Twitter strategy docs got leaked a while back, there was a specific section that dealt with potential lawsuits.

http://techcrunch.com/2009/07/16/twitters-internal-strategy-... (see Defensive Strategy section)

Legal

- We will be sued for patent infringement, repeatedly and often

- Should we get a great patent attorney to proactively go after these patents (We need to talk about this more, we are unsatisfied)