Well, many people have confirmed this problem is widespread if running X.Org Server 1.11 or newer. This is affecting users right now of Gentoo Linux, Arch Linux, Debian Wheezy, Fedora 16, users of the Xorg-Precise testing stack for Ubuntu 12.04 LTS, and other distributions updating their X stack in the past few months. It doesn't matter if you're using GNOME or KDE or one of the lighter-weight alternatives like Xfce. With a few hits at the keyboard (e.g. CTRL+ALT+Keypad-Multiply) the screensaver lock is rendered useless.
The first distribution that I saw taking action today was Arch Linux. Arch Linux acknowledged the problem and took the steps to correct it, per this bug entry. So next time you upgrade the packages on Arch, the vulnerability is no longer there for xorg-server 1.11+ packages.
The other distribution that's acknowledged the vulnerability is Ubuntu. In Ubuntu 10.10 they were very close to shipping X.Org Server 1.11, but they didn't due to the binary blobs (namely the AMD Catalyst driver) not yet supporting the latest xorg-server video ABI. If that was the case, all Ubuntu Linux systems would have been affected for systems going back to last October.
However, it's not until Ubuntu 12.04 LTS in April when they are upgrading to X.Org Server 1.11 (and not X.Org Server 1.12, which is expected for release one month prior). In the Ubuntu 12.04 "Precise Pangolin" repository at the moment is still the old X.Org Server 1.10 packages and other outdated X packages, but they have a PPA of the newer packages and have been preparing to push them.
In a new Ubuntu mailing list post today entitled "Smoke testing of Precise X server bits" it's mentioned, "A security hole will kill your screen saver if you type Ctrl+Alt+KP_Multiply - Will be fixed in xkeyboard-config upload in the next couple hours."
The Canonical comments were written by Chase Douglas. Yesterday Chase also referred to the X.Org Server to be found in Ubuntu 12.04 LTS as being a "franken-server." This is due to their use of X.Org Server 1.11 but they back-ported all of the input-related bits for Multi-Touch / X Input 2.2 back onto this older release.
Fortunately thanks to Canonical not shipping the X.Org Server 1.11 release this past autumn due to AMD's belated Catalyst driver, this issue isn't found in stable Ubuntu releases at the moment. Canonical is preparing to push their X.Org Server 1.11 packages (and Mesa 8.0 along with other X-related packages) to the Precise repository, but they acknowledge the issue and it should be addressed on their side by the time the merge happens.
In terms of Gentoo or Fedora or any of the other affected distributions at the moment, I haven't seen any activity today. If you have, please share the information within our forums.