We know that facebook just got a big investment from Microsoft see here:
Microsoft will take a $240 million equity stake in Facebook during its next round of financing, valuing the company at a whopping $15 billion.
Why? because facebook is the first operating system that allow ISVs (Independent Software Vendors) to write applicaitons that use social context. Here is one example that made me smile.
Hebrew Names. Allow you to simply send your name and get a picture of your Hebrew name. Try it.