After installing the Guest Additions I managed to get the screen resizing/ full screen functionality to work. However I wasn't able to share the clipboard between the Host and the Guest OS.
My next best option was using the 'Shared Folder' functionality which wasn't very intuitive
Firstly, the shared folders are made available under /media/ directory in the guest OS
Secondly, you do not need to allow sharing of a folder on the Host OS inorder to access it from the guest
Thirdly, in order to access the shares your guest OS user needs to be a member of the group 'vboxsf'
My Host OS is Ubuntu 11.04 and the Guest is Ubuntu 10.04.3 LTSSteps,
1) Start up and log in to the guest OS
2) Add yourself to the group vboxsf (System>Users& Groups)
3) Right Click the blue foder icon and click 'Shared Folders' or Devices>Shared Folders
4) Add a folder to share. Check make permanent (transient ie only available for this session didn't feel like working for me). Also check Automount.
5) Log out and back in to let the group permissions set
6) Browse over to /media/.. The folders that were shared should be available here
