Does it matter who is the one that submits your site to digg (i.e. are there more powerful digg users whose input counts more?)
It doesn't matter who submits your site to Digg, as long as they submit your site. There are some power-submitters on Digg, but it's not proven that they will have better results than submitting your site yourself. The best way to get results is to put unique and high quality content in your Digg articles and and have all your friends and family "digg" your articles to increase thier ranks. That'll catch more people's attention and bring you better results.
Zaccaria pretty much explained it for you and he is right. The reason some articles get more views than others is because of people "digging" them. There should be no difference in who submits them unless they somehow have friends that digg them when they post (which is typically frowned upon). Digg has banned countless people for submitting articles to their site then trading diggs from others just to boost their article. So, you should be careful and perhaps submit it yourself and hope for the best.
DIGG doesn't accept articles from GoArticles.com. So keep that in mind. I hear DIGG is also best suited for news-related or technology related topics. Yahoo Buzz! is good for more consumer related things: ringtones, cell phones, etc. So you may want to consider that, too.
I get my news from www.reuters.com They have RSS feeds and they have a formidable reputation of confirming news stories for Television news stations. A Very reliable source.
Here is a link to a post at Daily Blog Tips that I think can help you about Digg, as well as for Stumble Upon - http://www.dailyblogtips.com/qa-what-is-the-difference-between-digg-and-stumbleupon-users/ Hope that helps.
It is very true that it matters a lot who submitted your post on digg.. Suppose I'm a power user and I submit a post from your blog... Chances of making your Front page is very high... here are Two guides That will help you to understand digg. Digg : The beginners guide How to become power user on Digg
Submitting quality content from a nobody and waiting for it to hit front page is like buying a ticket from the lottery and waiting to win the big bucks.
People tend to follow the diggs of certain "power users" if they see new posts originating from them it will gain more exposure which will likely lead to more than an obscure person submitting it, so I would say it does matter who submits a digg.
The submitter is important because of the network (mutual friends and fans) the (power) user has. However, content is also important, and it comes right after the submitter (or even before) - if your content is not digg material, than even mr.babyman won't help you Techy stuff, and all that's news related - that's digg material (in a form of an article or a blog post) forum post for example will not pass even though it is highly informative forum post with 'enough' diggs. ...
The main way to get exposure is to get lot of digg .If your content is good you will automatically get a lot of clicks.
People don't care about those who don't always post useful information. There are plenty of "power users" who spew crap all day because they were paid to spew it. No one listens to them anymore than they do a new user. Sure, there might be a benefit in having a power user who has a following post your stuff. Generally though (from my experience), these people are not the ones that you can pay to have them post your stuff.
I agree with Anna B.'s post above, however off of that I would like to say I've seen alot of submissions fail because they try to be too much of a self promotion type post, compared to providing useful information to the users. You may get a few diggs out of it, but unless your content is extremely useful/unique/needed at the time or searched for.... people will probably not digg it that much. And yes, having alot of friends and basically a friend digging circle jerk helps alot.