Is using a lot of free third party libraries a good thing? [closed]

Question

For your proprietary projects at work?

Problems I can imagine are: more dlls (can be a problem when for example you have to include a big DLL but you only need few functions in that library), a lot of license statements you have to take care of when releasing your product, the reliability of the library, etc.

Any other potential problems? What is your opinion? (info: I'm using .NET at work)