carib and bzpilman gave some great ideas to link tasks to an online document, e.g at google docs, and other content via del.icio.us (cf. http://www.rememberthemilk.com/forums/tips/2934/). I would like to point out two other option:
Opening a google group and giving access to all people, that share a task or list with you, gives you the oportunity to upload any document, post the URL with a task. Now everybody working on a specific task can access the files he needs.
You can either put the URL in the respective field (URL) or you can include an URL or email address in a note. Saving a note will automatically give you a clickable link.
Posted at 5:33pm on May 13, 2008