Well the most confusing thing is to consider the right time to launch ppc. When should be the criteria for a sucessful campain, should we must wait till our site is fully optimised or as i feel that ppc has nothing to do whith optimization and link building
most ppc campaigns will be successful and kinda pickup when a site is optimized for searches as in an article directory, or a general directory of some sort, build your site to have lots of contents and activities.
I wouldn't wait until you are optimized, but I would wait until you have created the right landing pages for the keywords you buy. Of course, creating landing pages that are optimized for certain keywords works satisfies ppc and seo requirements.
SEO doesn't have anything to do with PPC. You should start your PPC campaign(s) when you site is ready for real live human visitors.