In an attempt to promote as much community as possible I would suggest removing the Website field for when people post comments to your WordPress blog. In this scenario below the Mandingo Theme is being used however it is just as easy to remove the Website field from the default field as well. If people still want to post their web site when making a comment they can do so in the body of the comment.
If you are using the Mandingo Theme then you will need to modify two files but if using the default WordPress Theme you should only need to modify one file. The lines to remove should be the same or very similar no matter what Theme you are using.
In Mandingo follow the below directions to remove the Website field from the comments form when people are not logged in.