Network effects are not indefensible. I don't understand why so many people in the bay area think that network effects are impossible to break in. Here is an example. Orkut. All my friends including myself were on Orkut in 2004/2005. By 2008 everyone moved to FB. Why? Orkut had horrible UX and buggy system. FB was breath of fresh air compared to that. Even though Orkut has superior privacy features (I still say they had best privacy features for any social app). FB is moving in that direction. It's quite buggy system and if FB must address the overall quality of application. It looks like Orkut in 2007.