Dare is back and writing like a madman. There's one aspect of comparing XML that I'm not sure he quite picked up, though

If I get arbitrary XML as input to my method and want to compare whether the XML fragment is equivalent to another XML fragment there isn't an easy way to do this without converting both in-memory representations to their string representations (if they aren't strings already) and doing a string comparison. Hmmmm...

String comparison is not nearly enough to determine equivalance. Aside from the namespace prefix mapping problem mentioned by Harry, there are problems related to order of attributes, whitespace between elements, and empty elements, to name a few. The Canonical XML recommendation has a good list of the issues. You have to decide what equivalence means when you are talking about XML derived data. If you want equivalence to mean "the objects that have been serialized as these two XML documents are equal in C#/Java", then you have more work to do at the "string comparison" level.