Its not that hard to get distracted during flight prep by pursers, redcaps, refuellers, engineers etc all sticking their heads into the cockpit, although MEL is probably not as manic as DXB. This was highlighted during the recent LOSA audit, but it seems nothing was done about it.
I have fallen prey to the "ZFW as TOW" gotcha and had it picked up by the FO or relief crew. Not only embarrassing but quite shocking when you consider the implications.
Now I estimate my Vref30 (Boeing) at preflight briefing based on the planned TOW. It's quieter and there are no distractions to mess with my already poor mathematical skills. I used to check my green dot speed (Airbus) as I recall we had a procedure to cross check it prior to entering the speeds in the FMGC. If my calculated speed is more than a few knots off the FMC/FMGC speed, I want to know why.
For A330 it was something like, Green dot = (TOWx0.6)+107 (This figure has to be increased one knot per thousand feet above FL200, but for takeoff this is obviously not necessary). It's quoted in Vol 3 from memory so you can check the reference.
e.g. TOW of 230t, green dot should be (230x.6)+107 = 245
For Boeing, Vref30 = (GW/3)+66 (this is accurate for the 777-300ER but will vary a few knots for other models).
e.g. TOW of 300t, Vref 30 should be (300/3)+66 = 166