Publishers can include a little snippet of code to let people with Digg accounts rate the article; you just click a "digg-it" button, and your vote is counted without you ever leaving the page.
Now when people come look at your page, they can see a rating (how many people liked the article) and it's added to Digg's database so people might find you through Digg's website under popular topics.
They also provide a service that lets you grab a "tiny url" that lets you share the article with a friend -- so rather than following http://conquent.com/bissellator/index.cqs?blogid=f8cfdef2eee3e4c33e71e68ea9aa6406 you can have a short URL like http://digg.com/d1xYTX
And here's where people are getting pissed.
There are lots of TinyUrl redirects out there (I referenced Conquent's own with the links above), and the expected behavior is that they'll just send you along to your link. Only now, Digg is stopping you on their site, showing you an advertisement, and offering other, similar content.
Honestly, I don't see any problem with this -- after all you're using Digg's service, server, and bandwidth, even if you are just bouncing off their server and moving along to the link. And this underscores what I had realized a long time ago: if you rely on a free, third party service to link to your website, you're handing those people the keys to your traffic. You're not building a bunch of links to YOUR site out there when you use tinyurl, or digg -- you're building links to them and trusting that they'll stay in business and keep sending your traffic along.
Digg provides a great, relevant service, and I think the folks getting upset about the "link hijacking" are just surprised -- remember Digg isn't hijacking a damn thing, you're hijacking THEIR bandwidth, and it's only reasonable to give a little something back to them and build a better, richer service.
Otherwise, install your own url redirect software. And if you don't know how, let me know and we'll get you hooked up.
Can you digg it?