From the Midday Open Thread at Daily Kos:
New Supreme Court Justice Elena Kagan has recused herself from 25 of the 51 cases the Court will hear, this term. She is doing so because of potential conflicts from the work she did in her previous role as Solicitor General. Her recusals speak to her sense of honor and integrity.
Justice Clarence Thomas did not recuse himself from the Citizens United ruling, which directly affected his wife's work at the politically active non-profit she founded. Justice Thomas also didn't recuse himself from the Bush v. Gore ruling, which also directly affected his wife's work. His refusals to recuse himself speak to his sense of honor and integrity.