With Debian, there are two choices for installing WordPress: install from WordPress’ package, or install from a Debian package. Both have their drawbacks.
WordPress’ package is the php source bundled up. After unbundling to the proper directory, there’s a couple of config steps and off you go. However, if you have 3 different websites, you must unbundle the source to three different places. And when an upgrade is available, you must perform the upgrade 3 separate times.
Using the Debian package didn’t work for me, so this is merely hypothesizing on my part. It appears the Debian packager for WordPress attempted to solve the multiple website issue: the php source is installed to a single location, and the config file loader has been changed to look for a file named wp-config-<site> in the /etc/wordpress directory. This would be great, if it worked. However, the first config step did not work for me (something about the database). I didn’t pursue this very hard. The drawback, and why I chose to install from source, is maintenance. With the Debian approach, I have to go to two sources for maintenance: either the WordPress site or Debian. If I were maintaining 100 websites instead of 3, it would be worthwhile.
I think the best solution would be if WordPress had a more elegant installation: installing the majority of the source in a common location that can be shared, and then the actual html directory would just be the config file and symbolic links.