It's really very easy to program against, and very powerful
However, it's not the easiest thing to find out information about - mainly because it's so young.
The pages I've found most helpful so far are:
- Scott Gu's original post - good for links to the base resources.
- Alex Gorev's blog - including the article linked here which told me how to do rich text labels
- The main Microsoft forum for the chart control.
- The SQL Server books online document a chart which is very similar ;) (but MSDN is a dog to navigate sometimes!)