The Pemex gusher ended with about 3 million barrels spilled (Wiki, I have not checked for more reliable information); about equal to the amount so far (guessing about 50000 bbl/day) from BP Macondo, and which will be some 7 million barrels if the offset wells are sucessful in August.

Yes, I agree, there were several warning signals from the Mexican well (and from Anadarko and other deep wells more closely related to the BP well); the blowout preventer failed at the Mexican well among other things.

Tony Hayward has admitted that blowout preventers need re-design (yet the base of the well was not properly secured- obvious carelessness by BP); the Macondo situation is orders of magnitude greater than the Mexican well.

Little is known about the formations below the deep salt layers although seismic gives enough data to identify some high spots- should have been a red flag here, as these highs often have high gas pressure.