Agile methodology is very easy once implemented. But implementing it is an organizational culture change.
We have see agile succeed and fail in several projects. Our implementation framework was developed based on our learning from these projects.
The first thing a company interested in implementing Agile should do is committing to the culture change.
While most managers thrive in their jobs by managing the deliverables of their staff well, Agile methodology tends to shift the control to team responsible delivering the product. The manager's responsibility shifts from assigning and managing tasks to ensuring that the team is not distracted from the committments made for a Sprint.
There are a number of products out in the world which all claim to be great implementations of the agile methodology, but installing a tool is not the last step of Agile adoption. The coaching is a very long process. Our experience tells us that for a well committed team, the coaching takes between 6-7 sprints before the team gets adjusted to the new process. Proper estimation, resource availability management and planning for emergencies are key in a successful Agile implementation.