I use Facebook to broadcast to my personal friends and local acquaintances. These blurbs and replies tend not to be as heavy on thought provoking content but I find that it's very useful for keeping in touch with that group of people.

Reddit has been good for me to talk to a wider range of people that are connected solely through common interests by way of carefully selected subreddits.

I just never really got into Twitter. I recognize it as a great tool but it just has failed to serve me and my particular needs I guess.

Youtube, for me, is usually a source of funny videos, instructional tutorials and informative clips. But I absolutely do NOT participate in the comments sections and I very rarely watch a video blog clip from there. So, I don't even really consider it a social network with the way I use it.

I really just hope Hubski will be a revival of the level of discussion that used to go on at Reddit. It still happens there and I will still browse and comment there but it's just been flooded out with attempts to find that perfect reaction gif or pun thread.