Start -> Search is a lot slower than Bam. The other desktop search products build a database, so the search is lightning fast. Windows can index files also, but most people turn the indexing off because it’s such a pig. And, as tkmt mentions, most searchers go through the Outlook data base (as well as other popular Email clients).
I use Google desktop. I find it kind of cool to just type a couple of key words. Google generally finds all the references quickly, be they in files (from any disk/directory), or emails. The one I want is generally near the top. It’s 1000 times bettern than Windows search. It’s uncanny that it seems to know how I want my keywords combined to find the reference. Or maybe all those years of web Google searches have unconsciously trained me to enter searches so that Google gives me the results I want. Either way, it works well for me.