Hello!
I upgraded Wheezy to Jessie using this method: viewtopic.php?f=66&t=1218.
The upgrade went well. There's just one small problem: I'm running the Android app "FolderSynch" to copy pictures from my phone to OwnCloud on my Raspberry Pi (Modell B). On Wheezy, this synchronisation runs perfectly in both directions. After upgrading to Jessie, the synchronisation app on Android stops after a few pictures and I get an error message saying "The target server failed to respond."
This is repeatable and reversible: if I reboot Wheezy again, the synchronisation works again without stopping.