[Spambayes] Spambayes with Courier MTA

[mike at ingenious.co.nz]

I have been trying to get spambayes working on a near-default instalation of 
Courier running on Ubuntu Linux.  I don't have a lot of experience with 
Linux, and am not sure how to diagnose the problem. 

The courier mail system works fine without Spambayes, and I can run the 
Spambayes script in a shell to train the database, but when I try to call 
Spambayes from the Courier daemon (e.g by adding DEFAULTDELIVERY="| 
/usr/local/bin/sb_filter.py | /usr/bin/maildrop" in courierd), if just hangs 
the daemon whenever a new mail item arrives. 

Any hints as to how to troubleshoot? 

TIA Mike