Soirees for this set are often celebrity-heavy and formality-light. You may already have noticed the need for the following.

• Invitation design with little copy.
  If there is too much to read, Gen X and Y are inclined to lose interest. Interactive, on-line invitations are more likely to entice than formal invitations.
• Use strong visuals.
  Bright colours in décor to interest guests who grew up on video games.
• Encourage participation.
  Employees with a MySpace/Facebook/Twitter mentality prefer to act instead of observe.
• Recognise the diverse span of a generation.
  “Gen Xers” who are on the tip of 45 and those 25 years of age are inclined to see things entirely differently.
• Include a post-party activity.
  For a demographic who likes to socialise, this can be a big plus.
• Never mention Gen X or Gen Y.
  To that group, using these phrases will be viewed as contrived.
  

Source: Eventline (updated)