I'm currently playing around with SharePoint 2010 but have come across an issue when using the standard Document Library and Announcement web parts. If I change the permissions to a list or library from inherited to custom permissions if a user doesn't have access to the list or library the web part displays the error shown below, instead of not displaying the web part to the user.
Web Part Error: Access denied. You do not have permission to perform this action or access this resource.
The thing thats confusing me is that the error only shows if the web part is within a web part pane, if I add the web part to a rich content area and a user doesn't have permissions to see a list it simply doesn't display.
If anyone knows how this can be resolved, please let me know. It looks like the issue dates back to SharePoint 2007 from what I've seen and have seen a technet article (919550) for SharePoint 2007, but does not yet say it applies to 2010 and have tried the workarounds contained within such as setting the target audience of the web part, but this has had no affect.
update I've since forwarded this issue to Microsoft who have been able to replicate the fault and are currently working on a resolution.