Having run tools like 'AltaVista Personal' and 'Enfish' over the years, and always having wondered 'why can I search a large chunk of the web faster than I can search my own machine', I've finally discovered one (at www.x1.com) that 'does the right thing': it's not merely that it indexes everything, but more that it displays incremental results in real time as you type (the set of hits grows & shrinks in real time as you modify the search terms. Ridiculously fast and useful – main download is free, license for advanced features (attachment search) is $40-ish;
*READ THE INSTALLATION LICENSE CAREFULLY BEFORE AUTOMATICALLY CLICKING 'YES'*
(the small print would appear to open the door to 3rd party adverts, implying either 'spyware' or a spyware hook … though users of the full product say it's fine — I run it at home and use my personal firewall to block it from accessing the internet anyway, and it works fine).
Frankly, it's so good that (a) I simply don't care about the license caveat and (b) it's inspired me to write this ridiculous email that sounds like a typical spam advertisement!