1. Steven picked Chrome OS as the web-centric distro, but I think Peppermint OS should be considered as an alternative. You can still use all of Google's services, but you also get the Ubuntu base and you have the option of installing lots of local applications as well.
2. For the second choice, a distro for someone that didn't want to learn much about Linux, Steven picked Ubuntu. There's nothing wrong with Ubuntu, but Unity itself can be a big turnoff for some people. If you're one of those people, one of the versions of Linux Mint might be a better fit for you. There are different flavors of Linux Mint, including Debian, KDE, MATE, Cinnamon, and Xfce.
3. I have no quibbles with Steven's third choice, a distro for someone switching from Windows to Linux, Linux Mint would serve very well in that situation too.
4. Steven's fourth choice of Fedora, for a user that wants "pure, hard" Linux was less attractive to me. Fedora is a fine distro and it certainly has its place for developers, but Debian might also be a good choice for those looking for a "pure" linux but who might not be developers.
5. The last section concerned KDE based distros. Steven's suggestions were good, but we might as well throw in the KDE version of Linux Mint too. Yeah, I know I sound like a broken record about Linux Mint. But the KDE version is quite good and should be considered by anyone needing a KDE based desktop.
I have one last suggestion to add to this list for anyone who wants a distro that contains only free software. Take a look at Trisquel. It doesn't get much press, but it's a very good distro in its own right, and it doesn't contain proprietary software. I did review of Trisquel 6.0 for Desktop Linux Reviews back in April, and found it to be a great choice for some users.
The Top Fifty Linux Distros
Speaking of Linux distros, EFY Times has a list of the top fifty Linux distros. The list is broken down into the following categories:
Distros Based on Ubuntu
Distros Based on Debian
Distros Based on Slackware
Distros Based on Arch Linux
Distros Based on Cloud Computing
Distros Based on Mandriva