I don't use System Restore, so I turned it off. I do not have apps installed that take more than a couple of minutes to reinstall.
1) If my computer breakes down, it's a sign telling me I've messed up too much and not just one thing. In that case I rather do a clean install, however that takes quite some time. I need a clean install once a year or so.
2) Because I need a clean install only once a year I'm not willing to sacrifice the amount of disk space System Restore requires.
3) I make backups of things that are important to me, so a full system crash (if I accidentily throw my computer through the window for example) doesn't hurt me (well, my data) that much.