Two problems:
1. When you try to subscribe an email via the sidebar widget, the email address doesn’t appear on the subscription list.
2. The export to csv file exports an empty file (only a header row and no subscribers or email addresses).
The first problem seemed to coincide with the upgrade to wordpress 3.3.1 and version 8.0 of the plugin (the plugin was upgraded first). In attempting to solve the first problem, I attempted to export the subscriber list to csv as a backup and reinstall the plugin. Now the list of subscribers is gone.