As for Oct'12 you can create your own custom addresses. Here is why you may want to do this:

1. The default auto-generated addresses are not human readable, i.e. username+id1-0c460fe2-feae-4513-b570-74a52e7b52dd+9ipr5fhh@inqloud.net so it is difficult to tell from the address itself which notebook it corresponds to. A custom address will look like this: myCustomWord+id1+ 9ipr5fhh@inqloud.net. You pick your own 'myCustomWord' prefix and hence make the address meaningful to you.
2. The custom addresses will resolve to a notebook plus a number of tags, that is when you send an email to a custom address that corresponds to NotebookA and TagA,TagB,TagC the email will be delivered to NotebookA and also tagged with the tags TagA,TagB,TagC
   

Configuring the custom addresses is easy:

1. Go to the 'Notebooks' menu
   
2. Choose a notebook and click the 'aliases' button
3. Add a new alias (custom address)
4. Once you have added your aliases, go back to the Overview page and hit Refresh. That last step will create new google contacts corresponding to the aliases.