http://www.youtube.com/watch?v=d-khx-i4YOI
 
These look really cool. Lately I've been up pretty late and relaxing by tying random knots before resuming homework. I usually pen spin too, but I've pretty much exhausted the activity. I haven't figured out contact juggling, and I've stopped doing origami a few years ago after doing it for as long as I remember.  
 
I'm thinking of making a begleri (fairly similar, but instead of the elaborate beads and silver chain thing, two weights on the end of a cord) to kill some time when bored.
 
Does anyone else actually do these?

I think that if you were in the same room as someone playing with those - inside ten minutes there would be murder committed.  
 
I can't think of anything designed to annoy another person more than those

I prefer a rosary.

That is an Arab thing.  On my first tour I worked out of both Kuwait and Iraq.  All the rich Kuwaitis walked around in their man dresses twirling those.  They are very interesting.  They have three sets of eleven beads separated by a flat bead called a "Shahid"  this is peculiar because that term is also used for a dead martyr.  They work the string three times for a total of ninety nine.  This has to do with the Muslim belief that there are ninety nine names for God and only the camels know the hundredth.  Everybody had different tricks and techniques and C_A is right, you get in a coffe shop with ten or fifteen of those guys and they will drive you nuts.  
 
  Odd side note.  I bought hundreds of sets of these made out of all kinds of materials, amber, ivory, coral, jet, garnet and even one made of rubies. I cut a lot of them up and made rosaries (I'm not Catholic) worn on the wrist and thumb.  Some I cut up and made regular bracelets out of.