We do a national (Gallup Q12) once a year, a few location specific for Best Places to Work, and we do a weekly pulse survey.  Nice pro about Gallup is that is gives scores and allows for benchmarking.  Also, the scores can be broken down by key areas including departments (so long as they are more than 4 responses) and year/year numbers/trends can appear.  Problem is no comments.  I rely on weekly pulse surveys to ask one question a week and this allows me to be more specific and capture comments and suggestions which we can use to enhance/tweak our programs and benefits and events.  (All surveys are anonymous.)  Downside of the pulse survey is that it's hard to benchmark to other companies but it is a great way to get insights and capture the voice of our people.

I think they can be great

It's just important to get the questions right, which should align with your ultimate end goal. From there you have to communicate the results and specifically what you CAN and CANNOT do. 

The toughest thing is decoding on a tool to deliver it. While free options can be cheap they take a lot of time to evaluate and get the set up right. The boxed systems are often expensive! 

I think culture surveys can be extremely helpful if you are prepared to take action on what comes out of those surveys.  I have been part of organizations that have conducted surveys and then never did anything with the responses.  This can be a real morale killer for employees.  Why complete a survey when your organization does nothing with the responses?