You're someone that wants to use Rails' remote forms, needs in-line error messages and doesn't want to waste a single minute building error management logic.
Until Optimism was released, you could only pick two of the above.
You can play with an instance of this project on Heroku.
This isn't an exhaustive demonstration that shows off every feature. For example, no attempt is made to show realtime, per-field validations because the implementation details are going to be different for every application. However, Optimism most certainly supports single-attribute validations; just pass in a single symbol or array of symbols instead of the post_params hash to the broadcast_errors method.