SharePoint 2010 Managed Metadata Columns and Metadata Navigation Settings

Ok, here's another one I don't get. I created a new Team Site. I added a few test documents to the Shared Documents document library and tagged a few of the documents with some managed keywords:

I go into the library settings to verify that the Managed Keywords column is of type 'Managed Metadata':

I want to use the Managed Keywords column to drive metadata navigation. I go into the metadata navigation settings for the library:

The description for the navigation hierarchies clearly states that a column of type Managed Metadata field can be used for the navigation hierarchies. Yet I don't see my Managed Keywords column in the list of Avaiable Hierarchy Fields. So, of course, it doesn't show up in my navigation tree:

I'm not sure if this is a bug, if the description in the metadata navigation settings is incorrect, or if there's some configuration setting I'm missing. But it sure would be nice if that worked. That's going to help the users a heck of a lot if it works the way I think it's supposed to.

Can't Edit Document Library form in SharePoint 2010

NOTE: I posted this about an hour ago but for some reason, it got deleted.

One of the features I looked most forward to working with in SharePoint 2010 is the ability to customize a list's add/edit forms in InfoPath. I created a very simple custom list and the ability to edit those forms was as easy as advertised. However, when I created a document library with all the default settings and without adding any columns, I got the following error:

The following is the full error text:

The SharePoint list form can't be customized with InfoPath because fields of an unsupported data type are marked as required, or because fields are corrupted. In SharePoint, try deleting the columns or editing the column properties to remove the required

Is this supposed to work for document libraries or is the ability to edit these forms in InfoPath 2010 limited to lists only? Like I said, I kept all the default settings and didn't add any additional columns to the document library so if this functionality is supposed to work, I would have assumed it would have worked at the very least in this scenario. But if it truly isn't supposed to work with document libraries in the first place, why does the command to edit the library's forms appear in the ribbon at all?