In its current state, the primary difference from between HN and Reddit is the content curation model. There aren't shared feeds on Hubski, so posts don't compete with each other for eyeballs. You do need to follow a few people to really experience Hubski in action. The way that posts propogate across Hubski is by sharing and resharing. If I share a post, it appears in the feeds of my followers, if they share it, it goes to their followers, etc...
There are other differences, but I think the significance of these other differences largely depends on the individual user.
As for future goals, I see Hubski as much as a publishing/blogging platform as I do an aggregator. There are a few hubskiers here that have developed a distinctive voice through the what they post and share. This is something that I have an eye towards for future development. This is also something a bit difficult to foster on HN and Reddit. In fact, based on our subscription model of content curation (and also the ability to ignore), we don't mind if users treat Hubski as an outlet for their own content. Users can follow it if they want, or not.
I hope that helps. Other users here might offer a perspective more valuable to you. Since I work on Hubski, it's a bit tough for me to separate intent from experience.
BTW, if you surround a user's name with @'s it will send an alert to them. Our markup is mostly based on bookending the text with a symbol.