After installing Kindle 3.4 (more than a week ago), my Kindle has become very sluggish. There is sometimes big lag between pushing a page turn button and the actual page turn, and even moving the cursor takes much more time. I do not have more than 50 books on my device, and I have verified indexing. After installing 3.4 I updated NiLuJe's jailbreak and font and screensaver hacks. I can't imagine that those things could have any affect on processor speed. I do have a launchpad and kindlepdfviewer installed. Also, I don't see how these could slow anything down.
I'm not the only one who has noticed this. I found it on the Amazon.com Kindle blog. I'm just checking to see if any of the hacks here could affect the new firmware.