v5 reached around 8,000 passing tests at the start of 2014 as an NQP project that needed a custom Rakudo and didn't have proper access to CPAN. FROGGS has since turned it in to a full P6 project which means v5 can now: use Rakudo's module infrastructure, and hence access CPAN with full P6 module management power; be installed via Panda; be hacked more easily.
(Rewritten to be more useful for folk reading this comment out of its original context.)
use v5 is a new (started April 2013) project aiming to build a P5 reimplementation.
It builds on Rakudo/NQP, a new open source compiler/ast/vm toolchain used to implement Perl 6.
Apart from writing "use v5;" at the top of files, using v5 doesn't require that you write or read any Perl 6 code. You just write Perl 5 code and run it. Results will of course depend on how far the project has progressed.
v5's current goal is to pass as much of the non-XS parts of the p5p perl 5 test suite as possible. It will likely take years to achieve substantial coverage, assuming it one day does. At the time of writing this comment it's passing 1,000 or so of the 40,000 or so tests in the suite. See STATUS for the current passcount.
The host compiler toolchain includes a backend which is slated to embed libperl and support use of existing XS modules. It's not clear to what degree, if any, v5 can or will be able to make use of this to extend its utility to cover scenarios involving use of XS modules.
The v5 project builds on parsing features (grammars) and a parser (STD) designed by Larry Wall.