What factors you consider in evaluating UX initiatives?

Hi,

As IA/UXUsability guys, We often face the situations of making decisions whether to implement new initiative or strike it off.

Ex: redesigning of an existing application, making your site compatible with mobile/handheld devices, implementing web 2.0/RIA style of interaction etc..

I'm interested in knowing how the IxDA community evaluates such new initiatives.

Please share your thoughts, any references to online resources.

Thanks in advance.

Hemanth