That’s left an opening for technology companies to become the targets of criticism.

Even as they hire aggressively and create innovative products, the initial public offerings of Facebook Inc. and Twitter resulted in new Silicon Valley millionaires, and in some cases billionaires. Among the newest: Facebook Chief Operating Officer Sheryl Sandberg, who last week became one of the youngest female billionaires in the world, according to the Bloomberg Billionaires Index. Twitter co-founder Evan Williams is worth about $3.3 billion, according the index.

On Nov. 7, the day of Twitter’s stock market debut, protesters gathered at its San Francisco headquarters, with signs like “We are the public, what are you offering?”

In 2011, Twitter considered leaving San Francisco, telling Mayor Edwin Lee that a city tax based on the size of the company’s payroll would erode its growth. Lee exempted Twitter and other companies from the payroll tax if they would move to Central Market, an area plagued by crime and drugs near City Hall. The microblogging site is now worth $32.8 billion.

Buses Blocked

Google, Apple Inc. and Facebook are among companies that have come under fire for busing employees from San Francisco to their Silicon Valley campuses, with residents claiming they congest city streets and use public transportation stops. A group of technology companies agreed in December to pay the city a daily fee to use existing stops.

Some buses have been blocked by protests, and in Oakland demonstrators shattered the window of a Google bus last month. News site Berkeleyside.com wrote last week about a protest that took place outside the home of a Google engineer in Berkeley.

The backlash has drawn the ire of members of the technology community, including Bryan Goldberg, founder of sports news service Bleacher Report, who wrote a satirical blog post this month defending tech workers, and former venture capitalist Perkins, who wrote a letter in the Jan. 25 Wall Street Journal comparing the treatment of the richest Americans to the persecution of Jews in Nazi Germany.

Perkins Comments

Perkins’s comments led his former venture firm, Kleiner Perkins Caufield & Byers, to disavow its co-founder, and venture capitalists including Marc Andreessen to openly criticize him. In a Bloomberg Television interview, the venture-capital pioneer yesterday apologized for using the word Kristallnacht, a night in 1938 when Nazis coordinated attacks against Jews, in his letter.