Well, it's definitely been more than 24 hours over which the 1.8 Skyrim game-update has broken the Creation Kit. My two cents is here:
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http://www.gamesas.com/topic/1420569-creation-kit-for-skyrim-18/page__p__21735149#entry21735149
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Now it's time for me to turn my attention to something that works properly.

Update.esm does not contain a lot of stuff, it does have race records though, among others.
It also seems to have a version number in its header when viewed in TES5Edit.

Does anyone know if Bethesda are working on a fix? or are they not even aware there's a problem, because it sure feels like it. A heads-up would be nice so I know when I'll be able to finish my mod. Can't even play the game either cause the mods I'm using no longer work. Tch...pay for a game you can't even play, that sounds just about right.

The same thing happens after every patch. It just takes a few days for the new CK to be released, be patient.

"A few days?". It's frustrating. I'd just, finally (I think), solved a problem I'd been working on for weeks when the CK died. I was just about to try it out. If it had only waited a couple hours more before updating.

One could use a http://www.mediafire.com/download.php?cq83aanf884421n, rename the real Update.ESM to 'Update.ESM.Real', then get back to work. Might wanna compare the results in TES5Edit afterward with the real Update.ESM after renaming the dummy to 'Update.ESM.Fake' just to be sure there aren't any oversights though.

Edit: Even better, just crack open the new Update.ESM in TES5Edit and change the version from 1.70 to 0.94. Dawnguard should then load in the CK with the new Update.ESM. I'd definitely check everything out carefully in the resulting plugin either way and switch the version back to 1.70 on *fingers crossed* Monday.