As a long time user of buildroot (uclibc) for several embedded systems, I have found it to be difficult to use and extremely unreliable. I lost count of the times that buildroot would fail during the build process, even with a minimal target selection. Also, the weird patching of the linux kernel makes it nearly impossible to use a current kernel.
I switch to a heavily hacked version of the DSL iso file for my development purposes. I also use a stripped verison of debian lenny with busybox for development.
I recently ran across tiny core linux, which turns out to be the exact lean development environment I have been looking for. I use tcl in a KVM/QEMU virtual machine to do the initial development, which includes kernel and application building.
Yes, the libraries are larger than uclibc, but the reduction in aggravation makes tcl the best solution I have yet seen for my purposes.