This morning I decided to make the heretical suggestion of using POD to replace rd2 for Ruby documentation (or use RDoc if you don't like either).
The reason? Both are markup languages and can be used interchangeably. I mean, I can use rd2 style documenation in a Perl module as easily as I can use POD within a Ruby module. The difference is maturity. POD has been around a lot longer and has a lot more tools, both in terms of output formats and parsing.
I'm now preparing for the kindling and match sticks.