With Rehnquist ill, all eyes are on who will become the next chief justice of the U.S. Supreme Court, including those of Harry Reid:

I think that he has been an embarrassment to the Supreme Court. I think that his opinions are poorly written. I just don't think that he's done a good job as a Supreme Court justice.

Everything I have read from Thomas appears to be of high quality. I can understand why Reid would not appreciate the jurisprudence of Thomas per the philosophical divide that separates them, yet in the same interview Reid had very positive words for Scalia, another conservative member of the high bench.

Although this is the first I have heard of the "embarrassment" critique, the primary argument against the capabilities of Clarence Thomas is that he is nothing more than a pawn or clone of Antonin Scalia. Five years ago, Daniel E. Troy wrote an article for the National Review which debunked this criticism. An excerpt:

One case that made the Post take notice of the Scalia-Thomas divide was Saenz v. Roe. At issue was whether California could try to stop being a "welfare magnet." The state wanted to limit recent emigrants from other states to the same level of benefits they received in their old homes rather than pay them California's more generous benefits. The Supreme Court, by a vote of 7-2, held that such discrimination violates the "right to travel," which partially rested on the Fourteenth Amendment's declaration that "no State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States." Thomas dissented, denying that welfare is a "privilege" of California citizens.

But he did not stop there. He charged that an earlier Court had "all but read the Privileges and Immunities Clause out of the Constitution" in the Slaughter-House Cases of 1873. As a result, later Courts have tried to read some of that clause's substance back in through dubious interpretations of the other clauses of the Fourteenth Amendment (the equal-protection and due-process clauses) — a tactic that has enabled the Court to reach many liberal policy outcomes that were not really entailed by the amendment at all. In the California case, wrote Thomas, the Court appeared to "breathe new life into the [Privileges and Immunities] Clause," but without addressing its "historical underpinnings or its place in our constitutional jurisprudence." Thomas then extended an offer that, if accepted, would radically reshape constitutional law:

Because I believe that the demise of the Privileges or Immunities Clause has contributed in no small part to the current disarray of our Fourteenth Amendment jurisprudence, I would be open to reevaluating its meaning in an appropriate case. Before invoking the Clause, however, we should endeavor to understand what the Framers of the Fourteenth Amendment thought that it meant. We should also consider whether the Clause should displace, rather than augment, portions of our equal protection clause and substantive due process jurisprudence.

To the surprise and mild chagrin of many conservative Court-watchers, Scalia joined the majority without comment.

I recommend reading the entire article, as it gives more evidence regarding the abilities of Justice Thomas than the 'embarrassment' statement of Senator Reid.

From what I see, hear and read, I prefer Thomas over Scalia for Chief Justice.