I am not a KDE user, but used to be, and after seeing so much about KDE4 I am really thinking about start using it again.
According to him as soon as it is released lots of distributions will start to offer it, well maybe that will not occur with my favorite Linux Distro (Debian) even though I am using Lenny in my Laptop.
Maybe Fedora, Ubuntu, Mandriva, Sabayon and others like those will offer KDE4 as soon as it is available, also CentOS is another issue, theses Systems, Gentoo, CentOS, Debian, which are more focused on stability will not offer KDE 4 as soon as it is available, but others focused on Desktop applications, as I said, Fedora, Ubuntu, Mandriva, will offer it as soon as possible.
That is of course my humble opinion.
Update: I was wrong in my perception, Debian will not be behind, please read here: