There is no such thing as Google Base. Yet.
We do have a rather compelling screen shot and a Google Blog post about the latest rumours.
I think it is likely that Google Base (and the name could change) is real. This is something Google would like to do. Google wants to index the world's information and a large community database is one good way to do it. There are pros and cons with a community database; as Wikipedia knows, a successful community database expands rapidly with a wealth of information but there is an issue as to whether the data is accurate. A wiki is good here as anyone can correct wrong information. A database with a single point of entry for each field is not likely to have that advantage. Google already has Google Answers where experts are paid to answer questions. This system has the benefit that the "good enough for the customer" answer is highlighted as accepted so other viewers can see the data had some worth. The screen shot of Google Base suggests you could add a "Database of protein structures" (this is a typically Googlesq example) and it certainly leaves me wondering how I can tell an accurate protein structure from one made up. There's the same problem on the main Google index, some could argue, but on the Web no page is in isolation. A page claiming to discuss protein structures and which is linked to by trusted authorities is more likely to be correct than a mess of a page which no one links to (that's how PageRank works, after all).
Classic. Here we find a blog posts which goes from discussing whether there might be - could be - will be a Google Base and concludes by discussing the pros and cons. We're still to see whether there will be a Google Base and we're certainly still to see how it works.