If I tag a link like this: http://shop.sitename.com/?utm_source=ExactTarget&utm_medium=email&utm_campaign=November2010
Can some variation of this tagged link follow a user from click to purchase? What if they click the link, go to the ecomm site, navigate away and go back 2 days later and purchase, can this conversion be tracked using link tagging like above?
Yes. Using segmentation, filtering or secondary dimensions, that info will be available to track until purchase, depending on your setup*.
By default, this information gets stored in the _utmz cookie, which is set to expire 6 months in the future. That means that unless the _utmz cookie gets overwritten by a different tagged link, the purchase 2 days after the click will be sourced to the initial click.
However, since this information does not preserve across browsers or computers, you should consider the data to be an approximation of reality, rather than a perfectly accurate portrayal.
( I say 'depending on your setup' because simply tagging links doesn't ensure that your analytics is properly configured. For example, if at any point in the purchase their domain or subdomain is changed, and your analytics is not properly configured, none of this will track correctly.)