Having now set up several sites using FSB I agree that some subjects struggle with the auto-population, but others get it spot on! As a result I now set up auto-population, leave it for a week (before going live) and then re-visit to see how it is coping. I then maybe tweak the Search criteria, including Keywords and Filters, or switch to manual population if need.
Even within the same site one category may work fine, but then I need to manually populate another as it just doesn't work out for that one. So at the moment I am now doing both!
Picking up on Roy's point on SERPS I would be interested to hear Carey's response as I too have found that after initial, very quick, appearances on page 2 of Google the site then vanishes. We all know how temperamental Google can be, but this seems to be a feature of FSB sites.