The main influx of readers is coming from TheoryofReddit and TrueReddit if I'm correct, and they are both decent communities. The real concern would be if a post was made on a larger and/or less considerate subreddit.
1) Syncretic griped in /r/TheoryofReddit 2) I needed 20 minutes to get my head out of my Mother-in-law's need to put fucking NFPA stickers on my 100%IPA so I ranted 3) Syncretic posted that rant to /r/bestof, where it became visible to 1.8 million people 4) 650 new users in 12 hours. Hubski is emailing me about 12 times an hour at this point from all my new followers. On the plus side, I'm not getting 100+ variations on "is not/are too" in my email, unlike my Reddit inbox. I'll be honest - I'd grown ambivalent about Hubski over the past few weeks and its inability to deal with controversy. However, when you've got 200 people expecting you to say something clever because your words brought them over the wall from Reddit, you feel a little obligated to provide. Look at it this way: the people who are happy with Reddit are not part of the new Hubski influx. And look at it another way: a big post on Reddit brings 600 new Hubski members. A big post on Digg brought a million to Reddit.
I think the number of new Hubski users is at about 850 now. The total population of Hubski is right around 5,000. So if you consider, they've had a nearly 20% increase in useres in the past two days. While it may not look like a lot "when put in perspective of the digg migration," that's not really the best comparision you could make. You're comparing an already-heavily trafficked website (reddit, which was not only 4k users at the time of the Digg debacle) with one which is, let's be honest, pretty small(Hubski - 4050 users 2 days ago). It would be a much better comparision if you could get a count on how big Reddit was before the Digg exodus and see how much it increased, via percentages or etc.
That post made it to the front page though... Meaning who knows who could be joining. That said, as of now I feel it's not an issue. The people that want to leave reddit are the ones that are sick of its nuances and most likely don't embody the obnoxious aspects that are killing reddit. Edit: spelling