Gentoo Linux is source-based distribution. It means whole system is compiled from scratch. But compilation is simple: Gentoo has Portage packaging system which makes compilation easier. For example: Installing&compiling postfix+fetchmail+antispam filter+clamav antivirus with all needed perl's modules is only about typing "emerge postfix fetchmail amavisd".
Gentoo is not for beginners, you have to set up all applications by hand (but it's not difficult :-))
List of installable packages: http://packages.gentoo.org
The distribution is clean, applications run faster and there are only packages you want.
Human HW req.: can read, can learn new things
Computer HW req.: It depends on Gentoo use (server/desktop). Generally say is faster than other Linux distributions due to compiling for your computer. Fast connection at least for installation.