I have just ran into the following issue:
When you open a document library which contains folder, the breadcrumb trail above the document library enables you to go back up into the folder structure. But when you show this library on a SharePoint page using a webpart, after going into the folder the only way to get back up is to use the “Back” button of your browser. In SharePoint 2003 the toolbar showed an “Up” button, but this button seems to have disappeared in SharePoint 2007.
Also when you apply one of the other masterpages which are supplied out-of-the-box (for example, BlueBand.Master) the breadcrumb trail which works in the default masterpage seems to break as well.
I think this might be an issue to be fixed in SP1 :-)