If you're accustom to saving Apple Mail messages as Rich Text or Plain Text and you're running the Safari 4 Public Beta then be aware that although saving these message will appear to work, nothing will be saved.
The workaround is to either uninstall the Safari 4 Public Beta or save messages as Raw Message Source. More information can be found in this Apple Knowledge Base Article.
It has also been our experience (Apple has not confirmed this) that sometimes we can not copy and paste text from Safari 4 Public Beta to Apple Mail. The workaround is to first paste into TextEdit then copy and past from TextEdit into Mail.
Contact us if you have any questions.