XML bad. Like fire.
But seriously. Unless it makes something a lot easier (e.g. web services interop)it's a bad choice. All the currently available XML readers are very inefficient. They use a ridiculous amount of memory and cpu. Some of the better (but not freely available) XML readers can chop tens of seconds of app startup (depending on the complexity of the XML). Even for simple XML, the current unmanaged MS XML reading dlls are bloated and slow to page into memory. The managed ones are better but are often the majority of memory churn in managed apps.