edit: Mods feel free to close, I discovered it was something unrelated that had also updated since the last time I played.

Ever since 1.4 the game has been unplayable for me and I assume anyone else who has multiple monitors attached to their computer (note: NOT trying to stretch the game over multiple screens, just playing fullscreen on a single display). The game is no longer properly constraining the mouse, so since my primary monitor is the rightmost one, if I turn too far left the mouse goes right out of the game and attempting to click for any reason (attacking, menus, etc.) results in Windows seeing a click whereever the mouse cursor has ended up and dropping me out of the game.

I have made a video to show the problem clearly: http://youtu.be/VFkxRxIaf-4

I have nothing but a default install from launch day, updated the whole way up via Steam. No mods, no INI tweaks, nothing but straight Skyrim as released. Steam verifies the game cache and everything, but the problem still occurs.

In case it matters, my system specs:

Windows 7 x64
AMD Athlon X2 6000+ (3.1GHz dual core)
4GB DDR2-800
GeForce 8800GT (driver 290.53, autoupdater says nothing newer is available)
2x 1680x1050 monitors, side by side.

edit: to make sure it's entirely clear, the game worked just fine and did not have this problem from release through 1.3, this is a new issue since 1.4.

I have this issue with many games such as SWTOR, SWKOTOR, The Sims 2, Bastion, and anything running on the Source engine, although I dont' currently experience this in Skyrim. Way back when the game first released I ran into a problem with the game not locking the cursor to the primary monitor, although it's since been fixed up.

There is a program known as Cursor Lock that I use for those difficult games. I'd recommend trying it out:

http://www.snakebytestudios.com/content.php?id=13

On the suggestion of a friend, I discovered it was actually the Raptr client's in-game chat overlay. Apparently Raptr also updated since the last time I played Skyrim. My bad, mods feel free to close.

I remember something like this with Wow, years ago. I have used dual monitors for years now and I haven't had any issues with games especially Skyrim, are you playing in windowed mode?