There definitely is. The wiggle room only shrinks to almost nothing when the case in question is one on which the judge gave advice as a government attorney; recusal is close to mandatory there. If the case simply involves an organization the judge was a member of, then it's much more within the judge's discretion. The problem with Miers is that she may have directly given advice to President Bush on the policy being disputed in a number of cases that come before her.
And then again, she may not have given advice on any cases that will come before the Supreme Court.