In Google Analytics, you can isolate segments of your traffic such as paid traffic, or organic traffic, new visitors or returning, Firefox users or Safari users using a specific report (such as New vs. Returning) or the Dimension drop down menu within reports. However, if you want to know it, only for a specific segment — in that case, set up a few profiles which filter down to these segments for your site. Google Analytics let you create 50 profiles per account, multiple profiles are a good way to view your data through different lenses and isolate certain segments.
Note: Just remember to leave at least one "real" profile where you don't filter at all.
Once you've learned to use multiple profiles and see data this way, you’ve the ability to learn more from your analytics. For example, you can create a profile that only shows paid traffic and you know that the Map Overlay report is only showing that visitor segment. In another example, you might need to know how visitors from a certain campaign reacted to the steps you set up in one of your funnels. Create another profile, filtering in only the campaign you care about, and looking at the Defined Funnel Navigation report.