Google is raising the bar again as they have been developing an entirely new version of the search engine everyone loves. Although most users will never notice the difference in results; Google boasts faster indexing speeds, more accurate results and a more comprehensive index. It is tough to say whether this has anything to do with Bing's activity, but I think it is clear that a little competition always yields improvements. The new dev version of Google is available for preview at: http://www2.sandbox.google.com/.
It is worth noting that in testing, I have found only very slight differences in the search results, mostly a difference in the speed and result set.