I've seen this type of script before. In my opinion it is kinda useless. I say this mostly because in virtually every browser you can click on the "View" menu and then choose "Page Source" from the list...which will accomplish the exact same thing.
As a matter of fact, I don't believe I've ever seen this code deployed on a professional site...usually only on hastily made blogs, etc.
I hand code all my pages, and honestly wouldn't really care if someone copied pieces of the code (ignoring php for a moment). Most of the time it is entirely specific to my page, so the amount of effort required to change/contort it into being used in something else would probably be close to just rewriting it from scratch. As they say, "limitation is the highest form of compliment."
If you are really concerned about keeping the coding of your site secure then you should either a) encrypt the entire thing and then parse it through a filter (this will greatly increase the cpu usage on your server, as well as requiring more time for the page to load); or B) purposefully write incredibly convoluted code that no one but yourself can understand (which is a waste of time, and probably won't be nearly as efficient as a correctly written page would be). In other words, I'd say both options are kind of a waste of time.
Just my 2cents.
Edited by gaea, 14 August 2006 - 11:31 PM.