I have been getting intermittent segfaults with Ruby Enterprise Edition 2010.01 on both Mac OSX Snow Leopard 10.6, and Centos 5.3 with LibXML:

/opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/gems/1.8/gems/libxml-ruby-1.1.3/lib/libxml/node.rb:57: [BUG] Segmentation fault ruby 1.8.7 (2009-12-24 patchlevel 248) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2010.01

See the LibXML Rubyforge page more details, but the solution is to code your document finders as below...

results = document.find('/') ... results = nil GC.start