ruby 1.8.6 uses ruby threads, not native(OS) threads. the "threads" use flag turns on only --enable-pthread, which is needed only if using tk, according to http://www.ruby-forum.com/topic/132550 and not using pthreads truly increased the speed ov the ruby vm. so i think a warning about that should be printed by the ebuild. thanks Reproducible: Always
People enabling the USE flag do it on purpose I think, also this becomes irrelevant with Ruby 1.9.1 anyway, so we won't fix that.