Facebook, Riverbed Technology and Google are among the best technology companies to work for, according to employee reviews compiled by Glassdoor.

And, here's the top 50 companies, listed alphabetically: The top 10 shared several characteristics, Glassdoor says: a solid company culture, opportunities to advance, training, a clear vision and transparency from senior executives, and s respect among employees. Besides leading the tech list, Facebook ranked first in the Top 50 list for all industries for the second straight year. Mark Zuckerberg had a CEO approval rating of 99 percent--but still ranked second among tech companies in respect, behind James Truchard of National Instruments. Microsoft's Steve Ballmer showed the most improvement, struggling up to 46 percent from 29 percent in 2011. That puts him far below the average CEO approval of 78 percent for tech CEOs . Ballmer can console himself with Xerox CEO Ursula Burns's continued seat at the bottom of the ratings: 21 percent compared to 23 percent last year. Also losing their popularity:  Netflix CEO Reed Hastings (42 percent this year from 63 percent last year), and Groupon's CEO Andrew Mason, who tumbled to 52 percent from 68 percent. Netflix's and Groupon's employees complained about long work hours and stress. Do their ratings mean anything for CEOs? Not necessarily, though Glassdoor points out they can act as a barometer of tension within the company. Take Yahoo's ousted chief, Carol Bartz. When she joined the company in 2009, she had an approval rating of 90 percent. By the third quarter of 2010, it had dropped to 50 percent. A year later, it hit 33 percent. We all know what happened after that.