How to make a view that only shows content a user has not voted on
An effective solution to this problem can be found in http://drupal.org/node/513088.

As suggested by Cthos, one should first set up a "Relationship" in the view setting ("advanced" settings in Drupal 7), then use this relationship as a regular filter (no need for contextual filter here).The proposed procedure is:

Relationships
    Node: Votes
        "Require this relationship": no
        "Value type": No filtering
        "Vote tag": Normal vote
        "Restrict to current user": yes
Filters
    (Votes) Votes: Value
        "Relationship": use the one from above
        "Operator": "Is empty (NULL)"