In order to have an anonymous-only FTP server that allows anonymous uploads, based on vsftpd running on Ubuntu 9.10, I applied the following configuration changes:

— /etc/vsftpd.conf.orig 2010-01-13 02:00:46.287216196 +0100
+++ /etc/vsftpd.conf 2010-01-13 01:59:34.787215294 +0100
@@ -26,16 +26,18 @@
#local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
-#write_enable=YES
+write_enable=YES
#
# Default umask for local users is [...]