There are no custom kernels as of right now, but they have built plenty of kernels for the Sapphire ROM for the Droid, so I'm sure we'll eventually see some good kernels for Ruby! This ROM is so fast anyway the only benefit a custom kernel would have is some undervolt maybe...
You are dead wrong on that my friend. With a modified kernel you can use scheduling to lower battery consumption, over clocking for more speed, undervolting for power consumption and heat, HAVS and AVS, and scaling. All add up basically to using the processor more efficiently which ends up in lower battery draw and a faster phone.
For those of you who haven't read up on King's kernels especially BFS here is a snip:
Also, a little info on HAVS and AVS:
The purpose of HAVS is to minimize the power used by the CPU by determining
and setting the optimal voltage. At the same time, the maximum voltage by
which HAVS can scale to is fixed to a specified voltage depending on the
CPU frequency in order to prevent scaling to a higher voltage than what is
normally used at a specified voltage. The optimal voltage is actively determined
for each frequency and temperature. HAVS actively adjusts the CPU voltage as the
CPU frequency and temperature changes.
Also with tackling custom kernels they can change the way it charges potentially etc. There is SOOO much a kernel can do for your phone. Hopefully we see some of these fine developers that know how to do them start working with the AOSP git's and push them out!
No as far as the Ruby, Cyanogen, and the other handful of AOSP roms floating around I have yet to test one that doesn't have some sort of glaring issue. Most of the time as of late it deals with either the bluetooth stack or the internal memory. I think most of them have figured out the camera's and gps dealing and all the basic phone requirements. Most of them all seem pretty stable as of right now on my phone, however there have been a handful of phones I have tried them on where they aren't stable and cause lockup's, reboots, or just don't work correctly.
So I advise anyone, as usual, make a nandroid backup and a titanium backup and play! The first Ruby was very sleak, I was equally impressed with this ROM it just felt like Cyanogen with some of the customizations missing. Hopefully these guys stay active and on top of things then I'm sure in a month's time we will have a pefect rom!