Is there a native notes app? I cant find it
There isn't a native notes app for the Nexus S because it doesn't have TouchWiz UI. I'm quite certain the voice action 'Note to self' actually sends an email to yourself (I don't personally use that action, not sure it likes a British accent)
There are loads of third party apps though. For example Scribb.it is full to the bursting with features, AK Notepad is quite a good simple one or Evernote has a strong following and quite a few more features.
The Touchwiz Memo app has been ported to ICS, you can grab it on xda (this is in the Vibrant xda forum sub-section, but it works on other phones).
This app works on JB too, you simply have to install it as a regular apk (not in system/app)