There are lots of people running around saying things like "Google Base squarely takes aim at Craigslist and eBay …" That is both narrow and largely incorrect. Google Base (and the related content that becomes available on Google) may ultimately have an impact on those sites. However, the company has a much larger and somewhat different vision for Google Base. (I've discussed this in my earlier posts.)
People have also been saying how Google Base is a limited or comparatively poor user experience (I made some earlier comments along these lines).
After chatting with Google about it, I think the company is not that focused on the Google Base user experience (although there undoubtedly will be refinements). Google isn't going to create hundreds of competitive vertical experiences around the data it collects.
My belief is that Google is profoundly ambivalent about verticals and wants to avoid them if it can. Google really wants to funnel or channel the data it collects from Base to existing Google sites. (That's not to say that Google won't face UI and other challenges in presenting this data.)
This is a big deal but content that might otherwise appear in classified listings on Craigslist or elsewhere is just a piece of the larger vision.