After reading OP's post yesterday, I decided to make the leap from SHOstock on my S4 to Task's AOKP. Task's ROMs have always worked well for me in the past, so I thought it would be a good choice.
Unfortunately, and this isn't necessarily Task's fault...on the leaked 4.3 that all the ROM devs are using, notifications for third-party apps are EXTREMELY hit and miss. The only notifications I could get were Gmail. Twitter, Facebook, Instagram, and Tapatalk just wouldn't push notifications at all.
The most frustrating part is that you can't really figure this out until you've gone through 2 hours of setup time after flashing the phone. I searched high and low for anything to tell me why this happened and apparently 4.3 has some different way of doing push notifications. I believe it will only be fixed once the app makers update the apps.
I searched through both the AOKP help thread and dev thread on XDA, and the only reference to push notifications was one post of someone mentioning the problem. In his typical ******* way, Task's response? Fully wipe and reinstall. Really? For something that should be mentioned in the OP of the dev thread? I've got an idea...why don't the devs stop jumping the gun and using leaks of ROMs as their base and instead use the older official firmware where you know things work? Is it worth it when there's little to no difference between 4.2.2 and 4.3? No.
So I restored my nandroid of SHOstock this morning and all's well. While I love using AOKP, you'll always run into these stupid bugs that are completely preventable.