A couple of months before the JB update came along, my Transformer Prime started getting very sluggish. There was a lot of lag and frequent hanging, and I had to cold shutdown a couple of times a week after the tablet completely froze up. I uninstalled a bunch of apps to free up internal storage, and while it seemed to get a little better after dumping a few GBs, that fix only lasted a few days before reverting back to sluggishness.
I installed the JB update knowing that I would lose Flash because I really wanted to speed things up. Unfortunately, there were only minor improvements. At times, apps would open almost instantaneously, and whenever that happened, I was impressed. However, this actually made the lagging feel worse, since the variance in responsiveness was now even wider.
I realized that the TP was initially quite fast and responsive out of the box and that the sluggish performance was a recent development that even JB could not fix. So I bit the bullet and performed a factory reset. After the reset was done, I ended up loading maybe half the apps I had previously, deciding to work on an “as needed” basis instead of trying to restore everything the way it used to be. The tablet was a lot faster, but I wasn’t sure if this was Jellybean or if this was the factory reset. I was trying to remember how fast it was when I first got it in January, but those details were hazy. Plus, it had just rebooted, so it wasn’t swamped with opened apps. I needed to have a couple of days to determine if JB itself had an effect on performance.
After using it for a couple of days, I think JB is making a significant difference with tablet performance. Apps do load faster, and the App List comes up a lot quicker and reacts much faster, even with 15-20 programs on the list. Before the JB update, I would hit the App LIst button and there was at least a 2 second delay before coming up. At times, it would glow blue, and then I would wait 5 Mississippi before anything happened.
The other significant improvement is that half the time, switching between screens is incredibly fast. The TP will pop between screens almost instantaneously. Unfortunately, I have had a couple of occasions when the Home Screen comes up blank and I have to wait a few seconds for the app shortcuts to populate. The number of times that happened has been reduced drastically, but it’s not perfect. And although it does switch very quickly half the time, the remainder of the experience is a one or two second lag between screens. However, when you take that all together, it’s still a big improvement in performance.
Note that a lot of people (including me) have a completely unusable camera after the reset. When I bring it up, the screen is all green with noise. Since I don't use the camera it doesn't really bother me, but YMMV.