If your plugin touches any of http://i.imgur.com/kzuTI.png records, you should probably ensure Update.ESM is a secondary master of your plugin to ensure you aren't inadvertently reintroducing a bug(s) officially fixed by Update.ESM. To add Update.ESM to your plugin's masterlist by checking it along with Skyrim.ESM in the File > Data window, loading, and saving. If uncertain, it's probably best to add Update.ESM as a secondary master. In the event you later determine it is not necessary, there are *ways to remove it.

*Delete key in File > Data > Parent Masters window

Note: Plugins introducing only new forms that are without edits to Beth records should never need Update.ESM as a master.

Query: I've never edited my SkyrimEditor.ini to my knowledge, yet I have always ticked both Skyrim.esm and Update.esm as masters, and my .esp's list them as such... Are they by chance falsely listing them?

Or... did I edit my .ini and forget?

*checks*

Nope... Ctrl+F couldn't find that line added to my SkyrimEditor.ini; false masters?

Thanks for this, I was just about to ask whether Update.esm was a necessary dependency.

Maybe I'm imagining things, but didn't one of the devs say something about not needing to set it as dependent?

Odd question... Update.esm is in my Data folder along with everything else, but it's not showing as an option in the launcher's Data Files list... so I can't activate it.
Might explain some odd problems I'm having, assuming it fixes a bunch of bugs.

Update.esm is hardcoded to be loaded (probably immediately after Skyrim.esm), so you're fine in that regard.

Oooh! That must have changed since the beta. Didn't even know >_< Just removed that line from my INIs and you're right, multiple masters can now be added/loaded without tinkering with the INIs.

*removes INI edit from OP*Wouldn't doubt it, but per http://www.gamesas.com/topic/1350270-q-about-updateesp-and-updatebsa/page__p__20348637__hl__updateesm__fromsearch__1#entry20348637, I brought up here with a link to the pic of Update.ESM's guts 'cause it's a valid concern. Most plugins aren't going to conflict with Update.ESM, so I'd agree it's probably not needed but for instances where the pictured stuff is in one's mod or if one just isn't certain. Given Update.ESM's inclusion in a masterlist is harmless, it just might be better for folks to include it. None of my plugins have it, but then again I always look at 'em with FO3Edit to make sure it's stepping on Update.ESM's toes.

Ah, cool cool. Good to know I wasn't crazy. Thanks for the info on this.