When does XP work...

I would never discourage moving towards XP if I thought the environment was right for XP. I tend to have the following criteria that must be met before moving in that direction:

-Small highly disciplined self contained team which includes end users of the system.
-Gurus in the technology and domain being used.
-The software built will be maintained and modified in the future by the same crew building it.
-A project manager that has the qualifications to create an environment for a very high quality communication network.
-Team members that are open to the XP intensity created in the environment, and are qualified to handle it.
-No outsourcing of any part of the project at all.

There are a lot of places I have seen that would benefit from XP, but it has been hard to get across to them that it is actually a strict process. TDD is viewed by many places as a process for setting up regression tests on modules already coded. TDD in it true context is a discipline that is hard to sell in many shops. Most people think XP opens the door to be able to create half ass documentation, have no real communication channels, and that it frees them up to use their own home brewed process and they just label it agile. They have taken parts of XP and morphed it into some mess that is not workable.

They don't understand that it actually comes with it own very strict rules and process steps that require the best of the best to implement.

I have found few shops that are capable, but would never discourage a shop that I thought was capable.

It always depends on the team, and the project the team has to be fit into. I use the UP most of the time. But I use it in a very iterative way. If the team is capable of handling XP exercises we will introduce them, if not we use the process to guide the team and do the opposite of what XP says, which is team (people) before process. In my opinion the team must be mature enough to handle the responsibility. I find few teams are.

I also run into more and more outsourced part of the project. Off-shore has eliminated the working software over comprehensive documentation. We need high ceremony documentation in order to set up a contract between the local team and the off-shore team. This falls under the guides in CMMI. We treat our off-site and off-shore teams as a contracting entity, and therefore must product the high ceremony documentation to allow for a thorough communication vehicle to be in place.

Like I said if XP is a viable methodology for the site I would never shoot it down, I just haven't found many places that contain the teams that are capable of the high degree of discipline required to pull it off.

More on XP, UP, RUP, etc. HERE