Nest is a product line which was purchased by Google, that includes a thermostat and Dropcam video surveillance system. These products are regarded as well designed and quite functional. While they're not cheap, the products are considered two of the more advanced on the market.
Each product is fairly easy to set up and aesthetically nice. They each have automation features and are far more advanced than the vast majority of security products in service.
So if the products are well designed and provide a quality service, what's the problem?
The problem is that Nest is a Google product. This sounds like a good thing right? The truth is that Google is in the home automation/security space for one reason, and that's to get information about Nest users. This means that all actions through Nest are tracked by Google. This data is of significant value to Google as it lets them understand the users living patterns. This invasion of privacy (and it is an invasion of privacy) allows Google to then use that data to create a full profile of their customers. They can then market to their customers since by understanding and documenting how the customer lives, they can sell that data to retailers.
Data about how customers live their lives is incredibly valuable to a retailer. To understand how they live at home gives you an insight that is invaluable. But as a Nest client, do you want businesses to know how you're living at home? Do you want them to know what you're doing? How many times you enter and exit your home? How you heat/cool your home? When you're home and when you're away? And do you want a company then selling that data?
A quality home automation company that is based on security, understands that customer data is not to be sold. They treat their customers with respect and will never sell any information to a third party.
Be wary of using a Nest Google system. There are other options at a lower price being offered by companies that will never sell your data. More people need to more cognizant of how certain companies operate and be protective of "big brother".