We present an AAOmega spectroscopic study of red giants in the ultra-faint dwarf galaxy Bootes I (MV ~ --6) and the Segue 1 system (MV ~ --1.5), either an extremely low luminosity dwarf galaxy or an unusually extended globular cluster. Both Bootes I and Segue 1 have significant abundance dispersions in iron and carbon. Bootes I has a mean abundance of Fe/H = --2.55 ? 0.11 with an Fe/H dispersion of Delta *s = 0.37 ? 0.08, and abundance spreads of Delta *DFe/H = 1.7 and Delta *DC/H = 1.5. Segue 1 has a mean of Fe/H = --2.7 ? 0.4 with Fe/H dispersion of Delta *s = 0.7 ? 0.3, and abundances spreads of Delta *DFe/H = 1.6 and Delta *DC/H = 1.2. Moreover, Segue 1 has a radial-velocity member at four half-light radii that is extremely metal-poor and carbon-rich, with Fe/H = --3.5, and C/Fe = +2.3. Modulo an unlikely non-member contamination, the Fe/H abundance dispersion confirms Segue 1 as the least-luminous ultra-faint dwarf galaxy known.