I have seen that before on occasion, when unlocking the phone, I think. The screen jiggles for about 1-1.5 seconds. No idea why. Doesn't do it often enough to duplicate and find the problem.
Never seen it or heard about it... If I was you I would have restored the iPhone to factory settings and then see if the 'Screen shaking' would go away if not I would take it to a apple store and discuss it with them (not that the apple store employee are much knowledgeable that people here at this forum )
I believe that you issue has something to do with the software or some modifications that you made in the settings so a restore should do the trick for you!!! Hope that helps...
Do you mean whenever you unlock the phone and all the icons come into place, the phone will seriously lag momentarily, but after that every things fine? If so that can be due to the ram being maxed out. Try closing some of your apps in the multitasking tray.