Actually voting “Yes”, I’ve now returned to a non-encrypted system, because of the drawbacks. Combined, they weigh more than the gained security I would get on my privately used phone.
The problem I’ve experienced right after encryption, was the incorrect handling of the SIM cards (detection problem, could not be activated or deactived in the settings), similar to the one described by @Chris_R.
Furthermore, I’m unsatisfied with the linkage of the encryption password to the screen lock password. This is IMO a security whole. Even if I change the encryption password separately afterwards, it will be changed back to the screen lock’s one, if latter is changed again. See also Changing Android’s disk encryption password on Android Explorations. By the way, the other screen lock options besides PIN and Password are not available anymore.
And because I’m switching off my phone quite often and also want to use the alarm clock, the missing wake-up functionality as described by @carpe_diem80 was the last straw that made me going through the backup-and-phone-reset procedure (fortunately the FP was not yet fully set up after my first three weeks with it).
Let’s see, how the system encryption develops during the next updates. Until then, I can live without it.