Here's some clarification about functionality:

N800/N810 (same bt hw, same bt sw, running os2008) has:
- BT FTP client functionality for fetching/browsing files from remote devices.
- BT OPP client functionality for sending files ("Send Via Bluetooth") to other BT devices.
- BT OPP server functionality for receiving sent files (pops up an UI dialog) from other BT devices.

The device does not have a BT FTP server, so you cannot e.g browse the mmc file structure from File Manager of another paired tablet. Below UI layer "gnomevfs" OBEX plugin is used for transfers, so if you don't like File Manager you can do tests with "gnomevfs-copy" command line utility.

As for the possible interoperability issue (IOP) with Treo. Maemo Bugzilla is your friend, and provide hcidump logs so relevant people may be able to help.