I keep a simple text file on my laptop. Since I take my laptop with me everywhere I go, it's not a problem to have it handy when I finish reading a book. Quarterly, I post a summary to my Reading Blog (
http://www.elsi123.net/~elsi/ ) Although I have accounts at LibraryThing, GoodReads, Shelfari, and even Delicious, I just update them periodically and keep the active file on my laptop.
Tompe, I'm interested in your SGML file. What markup system do you use? Do you have a schema?