NOt sure what my issue is with SwiftKey, but if I set it as the keyboard and reboot my phone 100% of the time it will go back to Samsung Keyboard. The only keyboards that remain set as default are those in the phone's ROM. I can use Swype (the pre-loaded one) and it never resets. If I use SwiftKey, it will reset everytime I reboot my phone, and additionally randomly during the day multiple times. It makes the keyboard unusable, so I uninstalled it and just use Swype.
I always factory reset and clear cache after any FW update that is a major Android update (GB to ICS or ICS to JB, for example), so that can't be the issue.
Never had any issue with GMail lagging. Phone is as swift as ever. That being said, I use Outlook.com for most of my email, so I don't spend much time at all in GMail.
I will note that most of the visual changes to my Skyrocket under JB make it look just like my buddy's S3. The difference is that his screen is slightly bigger in both dimensions, and so things (like the Notification Shade info) just look like they "fit" better. Even though mine's only 0.3" inches smaller, stuff just looks "shoehorned" into my Skyrocket by comparison.
That's the intent. It uses the same TW Nature UX as the Galaxy S3. Issue is, TW Nature was really designed for 720p screen resolution, and the GS2 devices only have WVGA (Samsung stayed with WVGA and didn't move to qHD like Motorola and HTC did). The lower screen resolution makes those elements take up a larger "effective" area of the screen than on the GS3. It is not that annoying on that phone, as it is on ours.
@ Simon Jones: My phone has 788 MB of usable RAM (not reserved for other things like GPU, etc.). Some of that used RAM is cached processes. It's code put there in case it's needed, but not necessarily running code. PCs do this. All modern operating systems do this. It boosts performance. If the RAM is needed, the unused processes are simply discarded to make room, and there is not much overhead for this since RAM is fast and the OS can theoretically do this without any extra work by just overwriting those areas in RAM. It is not really a performance hit, certainly not a big one. My browser certainly doesn't take 4 seconds to open. 1 second or less.
If you're constantly only able to get it down to 504MB, then I think you need to look into what applications you actually have installed on your device and troubleshoot with that as a start. I don't have many apps installed on my phone, so my phone doesn't tend to cache rogue apps/games that hog RAM.