Google Scholar announced yesterday a new feature to allow search within a citing articles.
Microsoft has also re-released the Microsoft Academic Search from MSR Asia. The MAS search has a faceted search interface which allows filtering by author, conference, and journal. In addition, it goes beyond searching papers by providing a page for each author. This is quite useful and it has interesting visualizations to show citations over time and connections to other authors.
It's great to see improvements in this area. Scholarly research is still far too difficult and we have a long way to go in making the search tools more capable.