Playing with social networks actually shows you how the world is small and connected. What really differs Xing from other nets I use is that they show the whole conection chain between existing connections and a person. Even when I had 1 connection (guy whom I met randomly in friends feed of my livejournal friend and afterwards met in Munich when I visited Friedrichshafen Outdoor trade show), all my IE contacts were connected with him through network. Random guy with my IE network! Well, Xing is the first system I saw that shows the whole chain (not like "somebody from your friend's network"). And even when I find my ex-colleagues from Norway, they are somehow connected with my IE contacts. Lovely!
Xing - 19 connections within 4 days (most from my university, 1 ex-colleague, 1 poutdoor contact, 1 from groups I added).
Odnoklassniki (Classmates) - 104 connections within 7 days.