For task management in the cloud there is a neat little (free!) app available: Wunderlist from the Berlin based company 6Wunderkinder. It runs on all common PC operating systems including iOS devices and Android as well as in the browser.
Please be aware that the sync function uses the cloud, so all entries are stored on Amazon S3 servers. So this is not a secure solution for private data – for the shopping list that might be okay. YMMV.
One drawback with the current version: there is no export available. Since I don’t like software with a lock-in I checked the local folders: on Mac OS X Wunderlist saves the data in the file ~/Library/Wunderlist/wunderlist.db, on Windows machines it is in c:\users\username\AppData\Roaming\Titanium\appdata\com.wunderkinder.wunderlist\wunderlist.db
Both files are SQLite databases which you can open with the SQLite Manager Firefox plugin.
With a SQL query you can extract the data from the tables „lists“ and „tasks“, join and export them to a CSV file.
Select T.name,T.done,T.note,datetime(T.done_date,’unixepoch‘),L.name From tasks AS T INNER JOIN lists AS L ON T.list_id = L.id order by L.name
The SQL query shown above is available for download as a textfile.
Update: In Wunderlist 2 the location of the SQLite database has changed, please see this post on cubewot.de.