You can do all sorts of magic with LVM, like backing up MySQL using file system snapshots, but in order to do so you need to set it first. When installing a new computer with Suse Linux I found that this was harder than expected, unless you know what to do. Needless to say, I didn't, but some friends gave me a hand on IRC, and now I do. :-)
So I wrote a little article about this which you can find here, in an effort to save others some time. The article is about setting up LVM with Suse Yast, but you can probably use it for other flavors of Linux, too.