I've tried updating F16 to F17 with yum again today,

#yum -v --releasever=17 repolist

Loading "langpacks" plugin

Loading "presto" plugin

Loading "show-leaves" plugin

Adding zh_CN to language list

Adding C to language list

Config time: 0.011

Yum Version: 3.4.3

Setting up Package Sacks

pkgsack time: 0.026

Repo-id : fedora

Repo-name : Fedora 17 - x86_64

Repo-revision: 1337941209

Repo-tags : binary-x86_64

Repo-distro-tags: [cpe:/o:fedoraproject:fedora:17]: r

Repo-updated : Fri May 25 18:39:56 2012

Repo-pkgs : 27,033

Repo-size : 27 G

Repo-metalink: https://mirrors.fedoraproject.org/metalink?repo=fedora-17&arch=x86_64

Updated : Fri May 25 18:39:56 2012

Repo-baseurl : http://mirrors.ustc.edu.cn/fedora/linux/development/17/x86_64/os/

: (15 more)

Repo-expire : 604,800 second(s) (last: Mon Jun 4 14:18:27 2012)

Repo-filename: ///etc/yum.repos.d/fedora.repo

The fedora reop is still in the "development" directory, not the everything directory.