After following the setup described on the Github page for rbenv and running the rbenv global 1.9.2-p290 command, ruby -v still outputs 1.8.7. When I try and run bundle, it errors because of the new Ruby 1.9 hash syntax, so I know that it is still running with Ruby 1.8.
I ran into this problem following the Vagrant Railscast. So this is in a Vagrant virtual box as in the episode.
Hm, this happened to me once when I had a stray .rbenv-version file lying around. Did you maybe create one by accident with rbenv local before? Or does the project you are trying to run come with one (although that would be strange if it requires 1.9 features).