Yes I do. When you have a team of developers with different model of how the system should work or works, it's usually a recipe for disaster. By modeling, we get to unify our thoughts and idea of the system.

When starting out a project, I tend to lean more towards well labeled conceptual diagrams. I will also use activity diagram, sequence and state diagrams.

While I have often read about people designing class diagram before hand, then writing or generating code. I never use class diagram before code is written. I use class diagram to document an existing system.

It's a tool, if you are willing to be flexible and realize it for what it is, then it's useful.