Good overview.

WRT to your comment about Google, I actually have little faith in their ability to innovate here. Google Scholar, as a simple example, is not very compelling. I use it very little.

I'd prefer to see them donate some cash or help (say for integration with Google Docs) to the Zotero project, which has both the talent and the vision to deliver.

For me as a scholar and developer, I consider it really important that these tools and data remain free and independent.
 

Bruce, thanks for the comment, and I agree with you about keeping these tools open.

I do use Google Scholar quite a bit myself, but usually in combination with library databases. My discipline is so cross-disciplinary that sometimes a quick Google Scholar search to give me some idea what databases to start with is useful.

I'm personally a big fan of Zotero. It works so nicely with just about anything.