I think this is probably the most mind-blowingly stupid and bad thing I've seen for a while.
There is no automated metric on earth that can get even a vague approximation of the value of a piece of programming. My colleague, yesterday, solved a fiendish long-troubling bug, by removing one character of faulty indentation from a 2000 line spaghetti routine. One change, one character and a comment. How would the system assess the "productivity" of that?
If SDI means anything, it's a rejection of the entire mindset that believes in the creation of, and use of, software in institutional control and measurement of employees. Bleaarrghhhh!
Update : someone from the company came back at me after I twitted (good for him, respect, obviously) ... but I went into full rant. :-)