I deployed some custom CSS tags into HtmlEditorCustomStyles.css in the 14 hive, and would have expected them to appear under the Styles drop-down for a Content Editor web part.
I've researched this, and found that they need to be prefixed with -ms-rteStyles if using the HtmlEditorCustomStyles but this didn't work either.
I also had a look at the RichTextEditor tag in my page layout to ensure that the ms-rteStyles are tagged and all looks fine.
I even did a hard reset of my environment, as a IISReset didn't do anything.
Can it honestly be this difficult to assign custom styles to SharePoint?