jnthn has an interesting post on the progress and problems of Rakudo's ng branch. Looking over some of the spectest files, it seems to me that ng has a good excuse for not handling many spectest files yet. By my rough count, at least 50% of the spectest files have a "rakudo skip" directive in them, ie a test Rakduo cannot handle. Because they have no equivalent "ng skip" directive set up, ng must handle every single case that Rakduo's master branch does to qualify it for inclusion in ng's spectest. If Rakudo master similarly had no skip directive, more than half of the spectest would be eliminated! So it's not surprising that ng is having growing pains on this front.
Personally, I'm quite impressed by the progress on ng. I cannot wait until I can use Perl 6's laziness -- that's a killer feature ng already has that Rakudo master lacks.