In no particular order of participation or importance:

• Facebook
  
• Twitter: short reactions to books & movies &, "ppetto"
• Flickr (organizing the shoebox, almost ready)
• YouTube & TeacherTube (experimenting now)
  
• Canine
  
• del.icio.us (when all else fails)
• wunK (arcane, abstruse)
• MySpace (abandoned long ago, is it still there?)