The goal of the IRA was traditionally to end British rule in Northern Ireland and form a united Ireland. While the terror campaign of the second half of the 20th century did not achieve this directly, it forced the UK government to the negotiating table (in largest part due to the bombings attacking London's financial industry), resulting in the good friday agreement.

This meant the end of direct rule from London, and the devolution of power to a Northern Ireland Assembly (including Sinn Fein), and additionally a statement that the question of a united Ireland could be decided by referendum in the future. With the protestant/catholic demographic projections the way they are, a united ireland result is not too unlikely in the medium term.

Regarding 9/11, there's good evidence that the aim was in fact to draw America into wars in the Muslim world (e.g. see 'the management of savagery', a purported Al Qaeda strategy document). In which case they could be seen as a success. However many commentators seem very sure of 'what al qaeda's strategy is', whereas in fact we don't know, so take that with a pinch of salt.

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