Do your unit tests constitute 100% code coverage? Yes or no, and why or why not.
Yes, I have had projects that have had 100% line coverage. See my answer to a similar question.
You can get 100% line coverage, but as others have pointed out here on SO and elsewhere on the internet its maybe only a minimum. When you consider path and branch coverage, there's a lot more work to do.
The other way of looking at it is to try to make your code so simple that its easy to get 100% line coverage.