Here, URL is the key and the comment is the value. You can use dumpdb to dump the database. A single database for the whole site. No need to create a file for each page. Easy to administer.
Users can edit their own hits.
If the browsers stop supporting this variable, the counter will break. Counter will show different values if the host has aliases and accessed via aliases. However, for the practical purposes it is ok as most of the hosts in the Internet is accessed by only one name.