We present updated predictions for the total production cross section of top-quark pairs at the Tevatron and at the LHC, and, at the LHC, of heavy-quark pairs with mass in the range 0.5 - 2 TeV. For t (t) over bar production at the LHC we also present results at root S = 10 TeV, in view of the expected accelerator conditions during the forthcoming 2008 run. Our results are accurate at the level of next-to-leading order in as, and of next-to-leading threshold logarithms (NLO+NLL). We adopt the most recent parametrizations of parton distribution functions, and compute the corresponding uncertainties. We study the dependence of the results on the top mass, and we assess the impact of missing higher-order corrections by independent variations of factorisation and renormalisation scales.