If you couldn't be there, io9 went to the Eternal Sunshine live read a week ago, and they've put up a good piece on the event. Makes me want to see the film again.

They comment a couple times on changes Michel Gondry made to the script. I don't think that's entirely accurate. Everything we've heard in the past indicates that Charlie and Michel worked closely together--Gondry didn't take the script and run, it was a team effort. That said, still a good article.

Probably the biggest change between the script and the film was that Joel’s ex, Naomi, plays a rather large role in the script. She’s not in the film at all, though scenes were reportedly filmed with Grey’s Anatomy star Ellen Pompeo. So here, actor Bridget Regan read the part and gave it a grounded sweetness that made you realize both why Joel loved Naomi, but also why they could never be together. Regan and actor Ryan Hunter each played multiple, smaller roles during the read as well, helping round out the cast.

Their shining moment came near the end of the story when Joel and Clementine are sent their Lacuna tapes. The script requires the two characters, who in the present don’t know each other, to listen to one another’s voices from the past, when they knew each other very well. How do you do that without overdubbing or recording? Well, Hunter and Regan read the taped dialogue as Starr and Thompson reacted to them, staying in character. It was a powerful, funny, and smart choice by Haley, whose every decision was absolutely spot on. (Source)