From the point of view of somebody who has gone through this
"This case involves an employee with knowledge of Microsoft’s sensitive customer and competitive information going to work for Salesforce.com, a direct competitor, in a job that is focused on the same solutions and customers,"
Yep. And a huge majority of cases where somebody is laid off or simply forced out of a company due to bad engineer/management relations (i.e., decides the grass is greener on the other side of the fence), this very same argument comes up. The (former) employee put several years of creative input into the former employer's line of products, then, being an expert in that particular line of product, is hired by a competing company.
Why should that person (who most likely has suffered severe mobbing, the wrath of managers who have no idea about what the person is actually doing besides the straight numbers and is not even interested in knowing) be kept from doing the same thing for the next company? It is not, usually, that the workslave shifting workplaces takes along intellectual property not thought up by him- or herself, but rather that the former employer would like to keep using those ideas, methods, in some cases patents (in which latter case there would not even be a problem at all!) exclusively. Which usually is ruled out in the employment contract. You can't buy a person's brain with a contract (well, not in Europe, the Commonwealth, the Francophonie or the US, far as I know.)
Back to the topic.
Any company that loses an employee who has such intimate knowledge of the business it is interested in that they would like to prevent this from happening, should do so by keeping on said employee at whatever cost it takes to do so.
If they can't be bothered to keep their cash cow happy, they at least should have the decency to let them go with dignity. Suing for IP after the fact is, in one word, ridiculous, and should be laughed out of court.
I, myself, at one point was put in a position where I had to negotiate with a former employer that had laid me off with extreme discourtesy. My new employer was in the same line of business. In the end, I won a settlement in my favour... though calculating the time and effort spent in getting there, I was pretty much shafted (had I been allowed to spend the time involved with gainful work instead of the ludicrous lawsuit, I would have made a few ten thousand quid more).
I need a crate of beer now.