First of all, there is no doubt that, during oral arguments, Sonia Sotomayor has a very gruff manner. While I think that this is a bad quality, and often borders on appearing arrogant, it is certainly not uncommon among federal appellate judges.
Moreover, people I know who work on the Second Circuit (clerks, administrative staff, etc.) or know her on a more personal level tell a different story. To them, she appears quite warm. Thus, there is some reason to hope that her behavior on the court - which seems "unjudicious" - does not carry over to her work relationships) behind the scenes. And I presume that the latter type of relationships are more important than how she appears in person.
Second, I believe that many assume she is more liberal than she is based largely upon her biography. In this respect, my experience is limited to criminal defense. In the cases I've argued before her (which is only between 5-10 appeals, I think), she has not shown any inclination to be particularly skeptical of government arguments.
Again, this quality is hardly uncommon; rather, it is the exceptional jurist who is willing to take a hard look at prosecution arguments. In addition, her views on criminal defense probably have little relevance to her positions on social issues, such as abortion or affirmative action. But, her views on criminal defense may say something about her willingness to challenge executive action.
Finally, I unfortunately report that her questioning style on the court does not suggest that she is an intellectual powerhouse. But I immediately caution that my opinion here is very subjective, and almost entirely framed by my relatively limited experience before her (but supplemented by anecdotal stories from colleagues).
More specifically, I have had the sense during my arguments that she does not always focus on the most important aspect of a case. And this makes me question whether she will be capable of presenting coherent, persuasive theories in opposition to Scalia et al.
My conclusion: I expect that Sotomayor will be a reliable left-moderate voice on the court, but will fall far short of Ruth Bader Ginsberg in terms of intellectual strength.
I hope I have underestimated her, and hope that my views are unduly shaped by the experience of dealing with her "gruff" exterior. The fact that Obama appointed her, in itself, is enough for me to wonder whether I have been unfair to her in the past. But right now, I think that we could have done better.
Just my two cents.
Just to balance things a bit, I thought I'd link to this pretty good discussion from SCOTUS blog, anticipating (and rejecting) arguments against her.
Also, someone noted that I did not really flesh out my conclusion why I questioned her intellectual abilities. The criticism is valid. But the reason for this is: (1) it is difficult to substantiate my impression that she has missed the point in prior cases, without going back into my records and launching into a very detailed discussion; and (2) my impression here is hopelessly subjective, and probably influenced by my personal involvement in my own cases.
Finally, I'll add that it is always difficult to discern any overarching legal theory from decisions by a circuit court judge, who is supposed to be following Supreme Court direction, rather than creating "new law." Sotomayor may well have some well-thought out, and even progressive, views that have not yet had the opportunity to bloom openly. We just don't know that yet. But I do believe it's possible to infer that she is not going to be a skeptic of governmental power in the context of criminal defense cases.