Unfortunately, it takes most search engines days or even weeks or months to index pages. This doesn't help you if you want to see what's being talked about today or in the recent past. But there are some new engines that help you tap into conversations as they're happening.
Check out Technorati. It monitors over 3 million blogs in real time so that searchers can see conversations develop as they happen. This is great tool for PR people and product management folks on the client side to help gauge reactions to a new product launch or recently-announced company news.
Similarly, I've used Blogdigger and Waypath with some degree of success to track emerging news and opinion. These engines tend to pick up the grassroots-level discussion that may take weeks or months to show up in the popular search engines. In many cases, smaller sites such as blogs often don't get indexed at all, so it's important to have tools at hand that can help track developing conversations.
Approaching the live aspect of the Web from a different angle, several new search tools allow users to see the most popular news and opinion that folks are talking about on the Web. What's Making Blognews? is a great way to keep your finger on the pulse of the early adopters, influencers, and opinion leaders. It shows most-linked articles across thousands of blogs and is a terrific way to see new conversations emerge.
I like this new trend toward realizing the immediacy of the Web. Some of these new search tools provide value in that regard, showing users new comments only moments after they are posted. Search engines, using their tried and true methods of indexing pages, can index pages only so fast. By the time you see a comment linked in a popular search engine, it might be too late to be actionable. Thus the need for these new tools to see what's being talked about on the World Live Web.
Could the major search engines pick up on this need for immediate information on developing stories and conversations, and integrate similar functionality into their offerings? Given that an early tip-off could mean the difference between a successful product launch and a thumbs-down from the early adopter community, I think the information is certainly valuable. Maybe companies like Google would want to improve their existing search tools by giving them more visibility into the here and now.