No matter how you slice it, getting to a million registered users is a pretty impressive achievement for Digg, a service that Kevin Rose and Jay Adelson and a couple of others started as a lark after TechTV shut down and Kevin was looking for something to do. It may be true that the million number has a lot of holes in it, as some of the commenters over at TechCrunch have pointed out — multiple accounts, etc. — but still impressive nonetheless.

A year ago, Digg had about 200,000 registered users, which means the user base has increased five-fold since then. Some of that could be a result of Digg’s branching out into topics other than just technology, but I still get the impression that the vast majority of what gets submitted to Digg — and certainly what makes it to the front page — is technology-related (I haven’t seen any data, that’s just a hunch). And Pete Cashmore at Mashable takes issue with the one million number too, in a post entitled “Kevin Rose Fan Club Signs Up One Millionth Member.” Louis Gray has some other numbers from other Web 2.0-type services, including StumbleUpon and delicious, both of which have over a million registered users.

The question in my mind is: how much bigger can Digg possibly grow? Could it get to two million users? Maybe. StumbleUpon.com is getting close to that. Could it get to five million or 10 million? I’m not so sure — especially if it continues to be mainly focused on technology, and the user community continues to be dominated by a particular type of fanboy/nerd/hoodlum personality the site has become notorious for fostering. Frantic Industries has a good post about Digg and the million mark here.

I think Digg-style features make sense for all kinds of sites, including things like Dell’s IdeaStorm. But whether the site itself is destined to get much bigger remains an open question. What do you think?

Okay, so Yahoo finally fronted the cash (reportedly about $10-million) for MyBlogLog, the viral social network that a couple of guys started awhile back and that has been growing by leaps and bounds according to Alexaholic. As you can find out from any of the bazillion posts on Techmeme this morning, there was a rumour back in November of such a deal, but nothing came of it.

That explains the nervousness with which people posted yesterday morning about another acquisition report, this time from a blog called Marketing Shift — which put up a post, and then just as quickly pulled it down. Om Malik posted something and then retracted it, but last night got to retract the retraction, after getting confirmation from his buddy Scott Rafer, the CEO.

My favourite part of this story, as told by Om, is that the two co-founders of the company are friends from elementary school, and that they raised zero — yes, zero — dollars in financing from angels or VCs (of course, it helped that Scott probably brought in some money from his previous stint at Feedster Note Scott’s comment below). Now that is a Web 2.0 story.

This is great for the MyBlogLog guys, and as I have written before I am a big fan of the application. I like the way it connects people who read different blogs, including mine. I like looking at the pictures of who has been reading, and then clicking on the pictures to see who that person is and whether they have a blog. That is social networking, pure and simple.

My only lingering question is: what the heck is Yahoo going to do with it? Their track record so far doesn’t exactly fill me with optimism about how they’re going to make use of their new acquisition. Don’t get me wrong — I like the fact that they haven’t screwed up Flickr or del.icio.us, both of which I am a huge fan of. But that doesn’t mean that owning them makes a lot of sense either.

How have they been integrated or made Yahoo better? The short answer is that they haven’t (my friend Stowe Boyd is similarly puzzled). Maybe Yahoo has a master plan that I haven’t been able to figure out — but I’m not betting on it. Tony Hung has some thoughts about what the company should do with it over at Deep Jive Interests. And Don Dodge does the math and decides Yahoo overpaid.