It's certainly easier for me to search one PDF file in Preview than a bunch of HTML files in Safari (and Google doesn't offer quite such focused searching). Both, of course, are more conveniently searched than is a dead tree.
Sun offer this apology:
Note: This online version differs from the final print version in minor ways, primarily the absence of quotations due to copyright issues. The physical book should be available in June 2005.
Which sounds to me like an additional reason to favor the PDF. I've never liked the pseudo-relevant quotations writers of books on programming languages are so keen on starting chapters with. It just reads like a sign that even the author thinks the book is dull and needs livening up.
I'd be more impressed if they spent their time factoring out semi-duplicate chunks of the specification, as they would if it were a program. For example: How do unary numeric promotion and binary numeric promotion differ, exactly? Is the difference between "In any case, value set conversion is then applied" and "After the type conversion, if any, value set conversion is applied" deliberate? Does "if any" mean "whether or not conversion occurred" or "only if conversion occurred"?
People complain about cases where the implementation is the specification, but at least that's unambiguous!