IPO fever seems to be back in Silicon Valley. On Thursday, wiki-review site Yelp filed to go public. It’s hoping to raise $100 million. Another online review site, Angie’s List, raised $114 million in an IPO that went out yesterday (OK, Angie’s List is based in Indianapolis, not Silicon Valley, but still…). Reports this morning say that Mark Zuckerberg has told the troops at Facebook that the social network’s S1 filing is coming “very soon,” perhaps as soon as next month. Finally, social game maker Zynga is expected to price is IPO shortly, although more questions could be raised about the company in the wake of this week’s management shakeup, which saw one-time chief revenue officer Owen Van Natta exit the executive suite, leaving 4.6 million in unvested options on the table.