Search user's all fileds in drupal 7
You can combine multiple field values into one (hidden) field using Computed Field. Be sure to save the value to the database, so that it can be used as a Views exposed filter. You'll also need to re-save each existing node in order to populate the computed field (VBO can do that in bulk).

This is another interesting idea (I haven't tried it): http://drupal.org/node/732458#comment-4750574