Digg.com is being blocked by filtering programs on thousands of schools across USA. I'm not sure this is the right thing to do given the fact that digg.com can be an inspirational website for lots of people including me. It's a phenomenon. It can be stopped. It shouldn't be.
I agree that there are some situations and cases when informations like the ones that you can usually find on digg.com should not be accessible to everyone or some people. I agree that porn sites or related ones should be blocked by such programs. I would rather block some categories by URL rather than blocking the whole site. Anyays, I've googled a little and I found many ways to digg and I think that we can bypass the filtering program.
Anyways, you can always google for "php proxy" or "online proxy" to find more results.
Let me know if it helps and...hey! Give this a digg! :)