Where kernel configuration file is stored?

Whenever you run make menuconfig, make xconfig, make XXX_defconfig, make oldconfig, make localmodconfig or any of the other make XXXconfig targets in the Linux kernel source tree, this creates (if successful) a file called .config. This file is used during the compilation of the kernel and is not erased unless you erase it manually or run make mrproper.

It's common to keep kernel source trees in /usr/src; if you did the compilation in /usr/src/linux-3.0.7 then your .config file is in /usr/src/linux-3.0.7/.config. (Since this is a dot file, the ls command doesn't show it unless run with the -a flag.)

Many distributions arrange to copy the .config file into the package containing the kernel, and install it next to the kernel, e.g. /boot/config-3.0.7 to match /boot/vmlinuz-3.0.7. Embedded distributions often don't do that; I don't know if Angstrom does, and anyway this doesn't apply if you compiled the kernel manually.

The kernel configuration can sometimes be available from the running kernel in /proc/config.gz. This requires the IKCONFIG compile-time option.

Your new one is .config at the top level of your kernel source tree. It may also get installed to /boot/config-3.0.7 or similar, depending.