My copy of the new C standard, ISO/IEC 9899:1999, finally arrived today, five months after I ordered it. This should (once I've spent a day or two carefully reading the whole standard) help in documenting the true status of C99 implementation in GCC and in creating test cases for C99 features and implementing or fixing some of them in GCC; up to now I've been working from a PDF of the FDIS plus the editor progress report on later changes. Done so far: many test cases, general clean up of C99-related documentation and parts of web pages, many fixes to exactly what features are allowed in which -std mode and to the -pedantic behaviour, many fixes to the printf format checking, the C99 names for long long limits in <limits.h>. Many other C99 features have already been implemented by other people.
I consider that the standard is worth buying and reading for every serious C programmer (though there will always be some people who make confident pronouncements about C on mailing lists and Usenet that bear no relation to its contents). Drafts and books other than the standard are best avoided for reference use. The Defect Reports are also useful to give an idea of problem areas in the standard. The PDF version announced on 18 July may suffice if you don't feel you want the "real thing" as printed and bound in Switzerland. The old standard in four parts is useful as well if you can obtain it.
The five month delay arose thus: I had book token prizes from Trinity College and wanted to buy the printed C99 standard using them; this meant going via a bookshop; ISO cause problems for bookshops by requiring payment in advance and not giving discounts. The bookshops I tried were unwilling or incompetent, even though authorised to mark up the price as necessary to cover their profit margins and costs: Heffers simply refused to handle ISO publications; Waterstone's took the order in February, but took four months after receiving a quote to get payment to ISO, during which time they more than once told me that payment had gone to ISO when it hadn't, failed to respond to emails or to email me when they had said they would, and generally didn't make any apparent progress until I got the manager of the branch involved (this is a criticism of their overall systems that failed to handle the order effectively, not of the individual staff involved).