Working on many sites, many projects causes the problem that I need to maintain, install, practically start new drupal installations very often. For example when I am developing a new contrib module I use a clean new installation (I call it "dev space") so no other experimental code interferes with my current work. Such a space usually has the same basic modules and outline: I always install devel module, use the same username/pw, set some user permissions so i can switch users back and forth, install admin_menu, add the php block etc.