First impression after ±1 hour: I want this on my daily driver, soon. Looks very promising.
Some un-recreatable glitches, but nothing serious.
+ Performance
is great so far, much more responsive than cm10.
I play Rdio from WLAN to my Bluetooth headphones while I play with the phone, and everything stays nice and smooth. CM10 used to have sound dropouts when WLAN is used.
Scrolling stays smooth when cm10 gets 'scratchy' on heavier web pages (I compare two rays side-by-side).
It is subtle but very noticeable: the scrolling stays closer too your finger; cm10 feels really sloppy in comparison (afaik this is a benefit of the v3 kernel, which is required for the full Project Butter features).
Apps start considerably faster (but this is a test phone, squeaky clean and brand new rom. I'll be very happy if it stays like that in daily use).
+ Compass works fine. This was unreliable, even with GB and stock ICS.
+ Google maps spinning arrow is ok now
+ it's cm10.1 (I was a bit envious of all the activity while the jellybean branch slowed down more and more)
Recreatable bugs:
- Power-button menu > turn on Airplane mode. From now on, the option is greyed out. (You can still toggle airplane mode via the notif. bar settings)
- About phone > Build date contains strange (Greek?) chars. Might be a feature

- ALS works but with a long delay (I think 10s hysteresis is ok for reducing brightness, but not for increasing - you'll be blind for 10s when you walk into the sun)
OP could say which gapps to install. (use 20130331, see next post)
Thanks Mike (and all other devs who are involved here)!
I really love seeing how suddenly there's so much going on with our 2011 phones
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update:
- ASOP keyboard is fine, I no longer need Xperia kb.
- gapps 20130331 works for this rom
- fyi, I really had to do a factory reset; usually I don't do that