With 4.3 comes apples implementation of address space layout randomization (ASLR). In short, this will mess up the way mobile substrate works. You will need a new mobile substrate in order to use your favorite tweaks such as winterboard, sbsettings, bitesms, folder enhancer, etc. So you should definitely avoid 4.3 until an official jailbreak is released for it.
but this thread isnt about jailbreaking 4.3, it's about the release of 4.3 and how "Great" it is.. i guess