I just tried to install the couchbase gem for RoR development. libcouchbase 2.0 beta worked fine.
me$ gem install couchbase --pre
Building native extensions. This could take a while...
ERROR: Error installing couchbase:
ERROR: Failed to build gem native extension.
/Users/me/.rvm/rubies/ruby-1.9.3-p194/bin/ruby extconf.rb
extconf.rb:25:in `block in <main>': uninitialized constant RbConfig::ARCHFLAGS (NameError)
from extconf.rb:24:in `each'
from extconf.rb:24:in `<main>'
Gem files will remain installed in /Users/me/.rvm/gems/ruby-1.9.3-p194/gems/couchbase-1.2.0.z.beta for inspection.
Results logged to /Users/me/.rvm/gems/ruby-1.9.3-p194/gems/couchbase-1.2.0.z.beta/ext/couchbase_ext/gem_make.out
OS X 10.8.1. What's the problem here?