At one point I was faced with a problem of downloading my Google mail using Web interface only (POP3/IMAP interfaces and forwarding were disabled for the sake of "security").
I found a project (a library) called libgmail.py that did just what was needed. Unfortunately, Google had changed the Web interface and the tool did not work anymore. The project at that point was abandoned as far as I could tell.
I wrote a Python module (Gmail.py) that deals with Google's Single Sign On solution and retrieves messages using Gmail Web interface. The second module (GmailFetchmail.py) receives messages using Gmail.py and feeds them to the local MTA (sendmail) to be processed using normal UNIX mail tools. The source code can be found here.
Before using Gmail.py you almost certainly would need to modify the source to account for a particular Single Sign On form details (the Gmail.login() method). You would also need to switch Gmail into Basic HTML mode.
Update: these days I just use Gmail Web UI and not bother anymore with offline readers. The point, however, was that I wanted to read my e-mail my way.