Here are the most revealing Roberts church/state memos readily available on the web. On p. 10 of the pdf, he offers a very subtle analysis of the conflicting opinions in Wallace v. Jaffree, a 1985 school prayer/moment of silence case. Roberts speculates that Rehnquists long (and, I think, quite compelling) dissent--aimed pretty squarely at the much-controverted Lemon test--was drafted as a majority opinion, but failed to persuade Sandra Day OConnor and Lewis Powell. According to Roberts:
Thus, as I see it, Rehnquist took a tenuous five-person majority and tried to revolutionize Establishment Clause jurisprudence, and ended up losing the majority. Which is not to say the effort was misguided. In the larger scheme of things what is important is not whether this law is upheld or struck down, but what test is applied.
Robertss implicit criticism of the Lemon test is quite consistent with the lines of argument I (and others) have found in our examination of the briefs he authored or co-authored. The contrast between Robertss doctrinally driven approval of Rehnquists efforts and OConnors disapproval could not be clearer and could not, to my mind, redound more in Robertss favor.
If you feel like reading more about these matters, see this WaPo article, which reports on memos not yet available on-line, and this overview, written by the Kansas City Stars well-regarded religion writer.