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To add to the thread, by the way I'm not moaning am just sharing my experience. While running 7-8 or more apps in the background. Start noticing a lot of lag and many of them just force quit. I'm sure this will be fixed as this is the first beta and problems like these are usual for now.
 
Big Picture stopped showing pictures after no.28 for me.

I have this issue even on my jailbroken iPad with the Virtual Memory hack. I think Safari just puts a cap on how much data it will cache at a time.
 
You know, honestly, I just got my iPod Touch 4G and have been playing with it lately. I am running over 10 apps in the background including Epic Citadel and have no lag what so ever. On the iPad I have a LOT [beta of course]. I am very optimistic about this because I remember same happened to the iPod 4.x beta. I'm sure once the final build is out - the multi-tasking will be rapid and won't provide any such lag experienced currently.
 
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