Ubuntu upgrades Kernel major versions to the latest available at the kernel freeze at every release. So, the features in 3.7 will hit Ubuntu systems with 13.04.
Arch Linux will probably get it in a couple of weeks.
Android, on the other hand, will take much longer. It's sad as there are so many goodies in this for ARM, especially the multi-platform support. This will make updating Android version a lot easier (for manufacturers, hackers). Right now the one of the bigger issues is updating the kernels (and the closed drivers, to be honest).
You can always blacklist a package (such as linux) in /etc/pacman.conf to avoid upgrading it during pacman -Syu, for example. I had to do this during a power regression in the kernel. However this isn't a long term arch strategy. Note also that arch has LTS kernels, should you prefer.
If not upgrading the kernel every week or two is a security hole, most people are pretty screwed. I personally do not like to restart that often. Turning off automatic updates just gives you control of when to upgrade.
If upgrading is not for you, ArchLinux is not for you. You should run a full pacman -Syyu at least once a week and clean up .pacsave files at least once a month. Probably even more often if you are on testing.
Ubuntu already has a generic 3.7 kernel (http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.7-raring/) in the kernel PPA. I'm already running it. Upbuntu usually has a shell script day of to download new releases. New Ubuntu versions are shipped with the latest kernel around the time of commmit freeze and just updates that line to avoid regressions in future kernel releases from harming systems inadvertently.
If you're rooted, you can often find custom, more up to date Android kernels optimized for various phones. (The android dev community being what it is, sometimes they're not optimized very well, but if you hunt around and find a good one, they can make a difference to battery life/etc.)
