Google Analytics can show you the keywords that people used to reach your site, it can also show you whether those keywords were paid or organic, it also goes into a lot of depth with regards to your Adwords campaign, how long visitors referred by individual keyphrases stay on your site etc.
So my question is, assuming that you use only Adwords and no other ppc services, is there any reason why you would want to use url striping? (eg. ?src=google&kw=example) What information could you gain that Analytics does not already give you? Or is it more something that people find useful if they are studying the access logs?