Not widely known publicly -- but within his colleagues' circles it is said his orientation is acknowledged and not paraded or denied. This was sort of an "outing" by the SF Chronicle in the way it was handled, though, even if Judge Walker was known to be gay. He was also selected at random for this case; nevertheless, I imagine the Pro-8 forces will indeed make the most of insinuations and attempt to discredit him and his ruling, should it go in favor of the plaintiffs (anti-8 ) He is a conservative judge, appointed by Bush Senior, after all, and his demeanor in court (according to blogs and transcripts) has been professional and unbiased. But that doesn't matter to the religious fundies/crazies.
How the Appeals Court and perhaps, should it be accepted, the SCOTUS justices deal with this "new" aspect and how they react to Judge Walker's legal verdict after his serious weighing of the two sides' evidence and testimony and amicus/animus briefs will nail-biting suspense for me and a lot of others.
However, in any other case, the sexuality or gender of a judge would surely be irrelevant and a non-issue (even in a rape case or a case involving an ethnic category if the judge were a woman or a man from that ethnic group).