well, lots of distributions are based differently... debian based, or whatever...
some use different kernels, and each distro usualy has its own kernel "enhancements"...
they usualy come with different things, since theres "TONS OF free software"...
i like mandrake, because of its ease of use, and easy to install...
it also has a lot of utilities that are exclusive to mandrake...
but basicaly most well do...