The lawsuit might be unusual, but it's not unusual for Microsoft to try to get companies to pay licensing for trivial patents in its portfolio. They've been engaged in aggressively pursuing licensing deals around their patents for a number of years: http://news.cnet.com/Microsoft--license-to-deal/2100-1012_3-...

Most of the time companies just pay up, as in the recent Amazon licensing deal. Salesforce apparently decided not to.

Both this situation and the one with Amazon also suggest that they are now specifically targeting online/SaaS companies.

expanding on "unusual" its only the 4th time they have done this.