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The OS memory imprint is bigger after a jailbreak. You will notice a slight decrease in performance.
 
No performance difference that I've noticed yet. I have SBSettings and LockInfo installed and that's about it (MyWi as well but that's just a regular app that wouldn't affect performance unless it's running).

I stay away from themes and changing icons and such, I think those type of things could affect the performance of the phone.
 
I have SB Settings installed and some emulators. No issues no slowdowns. My first jailbreak. Awesome. I honestly only will download the popular apps and won't change any themes just incase.
 
The OS memory imprint is bigger after a jailbreak. You will notice a slight decrease in performance.

No it isn't. Where's your proof of this? It's the applications and tweaks, not "jail breaking". Jail breaking just 'unlocks' your phone to customization, it's not a program that constantly runs to hog resources and slow down the phone.
 
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