I love the xml type in SQL Server 2005.  Here's a very simple way I made use of it: I audit all the object/schema changes to the database with a simple database-level trigger.

First, I create a very simple table (inside a schema I name 'Audit'):

CREATE TABLE [Audit].[Objects](

[EventID] [int] IDENTITY(1,1) NOT NULL,
[EventData] [xml] NULL,

PRIMARY KEY CLUSTERED
(
   [EventID] ASC
) WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

Then, the trigger:

CREATE TRIGGER [Trig_AuditObjects]
ON DATABASE
FOR DDL_DATABASE_LEVEL_EVENTS
AS
INSERT INTO Audit.Objects(EventData)
SELECT EVENTDATA()
GO
ENABLE TRIGGER [Trig_AuditObjects] ON DATABASE

That's it.. now I get a nice neat little xml entry in my table every time a DDL database level event happens, like so:

<EVENT_INSTANCE>
    <EventType>ALTER_TABLE</EventType>
    <PostTime>2007-06-03T20:12:05.813</PostTime>
    <SPID>55</SPID>
    <ServerName>CHI100906</ServerName>
    <LoginName>MYDOMAIN\myusername</LoginName>
    <UserName>dbo</UserName>
    <DatabaseName>Sales</DatabaseName>
    <SchemaName>dbo</SchemaName>
    <ObjectName>Products</ObjectName>
    <ObjectType>TABLE</ObjectType>
    <TSQLCommand>
        <SetOptions ANSI_NULLS="ON" ANSI_NULL_DEFAULT="ON" ANSI_PADDING="ON"      QUOTED_IDENTIFIER="ON" ENCRYPTED="FALSE" />
        <CommandText>ALTER TABLE dbo.Products
    DROP COLUMN testremove
       </CommandText>
  </TSQLCommand>
</EVENT_INSTANCE>

The EVENTDATA() function is provided by SQL Server inside a DDL trigger and provides all the data you see above as an xml document.

I like having this during development - it's like a poor man's source control for my schema changes.  But also, it could come in very handy for forensic purposes when diagnosing post-rollout issues or accidental schema changes.  Anyway, it's simple and handy for what it does.