Judging from the tweets during and after the show and from the first magazine reviews showing up... X certainly rocked Lollapalooza! Here is the setlist:
• Rusty Nail
• Jade
• Kurenai
• I.V.
• X
• Tears (SE)

Check Lollapalooza's Flickr for some amazing pictures!
You can find reviews on Chicago Sun-Times, TimeOut Chicago and USA Today.