acceptable when using javascript?

[eluser]dottedquad[/eluser]
Hello all,
When is it acceptable to use javascript and when it is not acceptable? For example I created a form and perform the first set of validation on client side. When client-side validates javascript then sends the form values via AJAX/JSON to the server-side, but I haven't gotten that for yet. I'm hoping to fulfill this need using Codeigniter.

-Rich