[nfriedly]

+1 for Buildroot!

I haven't done much with Yocto, but I had very good experiences with Buildroot, particularly with getting helpful answers to noob questions I posted on stack overflow. One was answered by Thomas Petazzoni who, I think, is one of the main people behind Buildroot.

[eschneider]

I've used both in commercial products and I find Yocto to be more flexible than Buildroot, but the learning curve is less with Buildroot. Still, both get the job done and are reasonably documented and supported, so pick your poison. :>