Greetings from Singapore! I'm here attending a training course on MOSS Administration, but more on that some other time. Right now what I've brought you here to talk about is WSS Search. So it is common knowledge that the search technology has changed between version 2 and version 3. In version 2, WSS used SQL Server full text indexes. Now WSS uses the same underlying engine for indexing content as MOSS.
However, what I feel isn't common knowledge is how this affects the end user experience. When you performed a search in WSS 2.0 you could only get results back from the document libraries and lists in your current sub-site. You don't see results from any sites underneath it. In WSS 3.0 it's a very different story. Not only will you see results from any child subsites, you will also see results from any site collections located underneath the sub-site you are searching! Surprised? I was.
So this means that you can run a search from the very top of your website and it will search the document libraries and lists in all your site collections. The results are still security trimmed. Nice.