I find them very useful. I don;t do web development regularly so I tend to forget some of the technicalities, i.e. form submission, PHP functions and database access. I find this site has some great no-nonsense tutorials that not only serve as refresher courses for things I am rusty in but can also bring me up to speed fast on stuff I haven't learned yet. This helps get things done faster so I can spend more time on things I am really intersted in. Of course web programming (and programming in general) can be enjoyable as well.
http://www.w3schools.com