Event Validation - Is it truly necessary for Js Heavy applications

Question

This thing is really show stopper, i've been thinking about event validation and is this really necessary. I am looking into ways to avoid event validation for building a webservice-javascript oriented page where dropdownlists are loaded based on webservice data. I could disable event validation for the page but i would like some insights(mostly how you think they might do it) as to how biggies like Google, Yahoo perform such validations. These organizations are hugely public based and use web services for almost all their services, rely heavily on ajax for making their things simpler.

How should i validate the post values in the case, event validation is disabled.