@ alexban:
That's what I thought: If that wind in the PERF INIT page was named "TOC WND" instead of "CRZ WND" everything would make perfect sense to me. As was already mentioned here before, the wind at the TOC can sometimes differ significantely from the average wind, but from the information I have on this topic all that this insertion does is change the climb speed - the FMC wants to get the airplane up into a tailwind as quickly as possible and stay out of a headwind as long as possible in order to improve economy, depending on the cost index. That's also the only information on this specific question in Bill Bulfers FMC manual.
In fact, is there something like a FMC manual written by Boeing?