In my opinion you should package libicu with PI to be sure that you get the exact version that you would like to see. Also PI should work on standard installs of the supported Linux distros without requiring additional installs.
When I try to install libicu on Fedora17, I get this:
$ su -c 'yum install libicu'
su -c 'yum install libicu'
Password:
Loaded plugins: langpacks, presto, refresh-packagekit
updates/17/x86_64/metalink | 18 kB 00:00
updates | 4.7 kB 00:00
updates/primary_db | 7.3 MB 00:13
updates/group_gz | 439 kB 00:00
Package libicu-4.8.1.1-4.fc17.x86_64 already installed and latest version
Nothing to do
Checking with "ls" shows it is actually there:
$ ls /usr/lib64/libicui18*
/usr/lib64/libicui18n.so.48 /usr/lib64/libicui18n.so.48.1.1
So apparently the lib is there, put PI does not pick it up (presumably it is looking for some other version).
Georg