We have added a subsite (/usa) to an established global website. This subfolder has been made region specific to USA using google webmaster tools. Now we want visitors from USA to be automatically redirected to this subfolder based on ip (standard 302 redirect). So far so good. Now, since the global homepage still remains /, we want the redirected user to still be able to visit this page if they click on the 'global home' (/) link. To be able to distinguish that this user should not again be redirected to /usa, the only option I can think of is using session.
So the question is, if this session based redirect is acceptable with the search engines. We are not going to be considering bots separately, so since the bots don't work well with cookies/sessions US based bots will never reach the global home. How will this affect us? We definitely don't want to lose any of the existing value of the parent site because of this change.