Two cases from the Eleventh stand for the proposition that the Court will indeed give defendants the benefit of Booker when it absolutely must.
One was a revised opinion in US v Garcia. When the original opinion came out, I noted here that it looked as though the panel was perhaps being more generous about waiver/abandonment than some other panels have been. The new opinion, though, makes clear that the relevant defendant had made the Apprendi argument in the District Court, had made the same argument under Blakely in his initial appellate brief, and had then made the same argument under Booker when that decision arrived. So, the issue was perfectly preserved and had to be reached.
The other is an opinion on panel rehearing in US v Custer, vacating Custer's sentence under Booker because it contained enhancements based on non-jury findings, where (as with Garcia, above) he had raised the issue in the District Court and in his initial brief on appeal.