Regshot is the little registry utility that could. Able to do a full registry and directory scan before and after any event, it spit out a detailed HTML report of the changes to your system all in a measly 72kB of .EXE goodness. Not only is it one of the most useful utilities around, it probably packs more usefulness/kB than any other software I know.
Its problem has always been unreliable hosting. It has lived its online existence hosted on endlessly different servers, moving around more than a Mongolian nomad (and thus limiting its fame, along with the fact the developer is Japanese and thus less well know in the anglosphere). But it looks as if the nomad is trading the tent in for a shiny apartment in a large co-hab block; Sourceforge:http://sourceforge.net/projects/regshothttp://regshot.blog....glepages.com/regshot
Please make sure you have enough bandwidth to download the latest version, 90kB including full source. Maybe I should set up a torrent?
 Of course proper standard units are usefulness/KiB