Do you have a favorite blog where you'd like to be notified by email when it's updated, but the blog owner hasn't implemented an email notification feature? If so, what can you do? Sure, RSS readers are an option, but what if you much prefer email? That's where a number of services, like RSSFWD, SendMeRSS, Feedblitz, and (though now defunct as of Feb 2007, it seems) Squeet come in.
They're free services where you provide them the RSS URL for your favored blogger and they will notify you when it's updated. Very nice solution to the problem above. RSSFwd even offers a bookmarklet you can add to your browser toolbar to make it even easier. Just visit a feed URL, click the button, and you'll be shown the RSSFwd page filled in with that URL.
And if you're a blogger, wishing you could offer a way for folks to get email notifications of your blog, some also offer a means for you to add such an option to your blog, again for free, of course. (Another way to solve that is bloglet.) I'm sure there are still other similar solutions out there.