PY and KT, you make a valid point, but what I feel is often missed in these discussions is that Liam, myself and others who point-out the strength of opposition aren't dismissing runs scored against weak opposition, we're just saying "take them in context".
Hayden's 380 was scored against Blignaut, Ervine, Price and Gripper, plus a hopelessly below-par Streak. Not an attack that's likely to make scoring runs especially difficult. Plus, rumour has it he should have been lbw 1st ball.
Lara's 375 was scored against an attack including Fraser and Caddick. Neither of these were quite on top of their game, but both certainly bowled better than Streak did at The WACA. Hence, Lara's runs were harder to score, because the deliveries he could score off came around less frequently.
Ponting in 2003 faced bowlers of the like of which would have been mincemeat to Gavaskar as well. Therefore it should not be assumed that because Ponting scored more runs than Gavaskar did in 1979 he played better.
Runs should never be dismissed - Ponting's was a good achievement, so was Hayden's, there is no denying that. Any chanceless Test century is a good achievement. But achievements must always be taken in context, and when comparisons are made the context should always be remembered.