gratz! i will make up my mind too to flash hacksung's ICS this friday, which is also my birthday!!! XXJVU with value pack is very very buggy, phone.process always crash right after you end a call, then now front camera can't take picture, some picture taken while in recording video can't be view, lots of problems.... or is there any fix to this?

just sync your calendar events to gmail.

flash to new ROM, then sync it back down from Google.

gao tim.

Custom since it make twice on stock

the signal icon will only turn blue when you connected to google through data or wifi. even it is a blue theme you need to connect to internet only it will turn into blue. well, for the clock i think you need to ask the theme's developer.
for simple understanding, here is some steps you can follow.

1. flash any stock rom for example XXJVU using odin.
2. go to xda and download any custom kernel like semaphore which is compatible to your rom. by flashing custom kernel you will get root access. without custom kernel it is not possible for you to flash any custom rom because you need cwm in recovery.
3. flash any custom rom or add-on script or theme which is compatible to your rom. ( with or without is ok)

if you want to flash custom rom you can straight start from point 2. if you want to go to stock xxjvu then you start from point 1. make sure you are clear with everything before you flash.

I use SMS backup & restore to restore my SMS after flashing, and to import/export contacts(send namecard via email) , I select all of them and send them to my gmail, and then restore it by downloading the namecards.