Share your experience!
Note: Additions added in an editing step are set in blue italics.
Last week, our TV prompted us to allow a firmware upgrade to 6.6545.0255EU. Bad move.
a) Since then, the reception quality via DVB-C has degraded to inacceptability on several, but not all programs. At the same time, it is hardly possible to select a different signal source, it looks like the CPU is occupied completely by attempting to correct the image. If there is a longer still image scene in the program, the image improves but breaks at the next content change
b) The hitherto flawless Ethernet connection (via LAN) is not possible any longer - A static IP address that I enter is not stored, instead, the TV attempts (and obviously memorizes) a different one all the time (programmed: 192.168.1.128 - the connectivity check - that fails then - says it looks at 192.168.1.49. Not surprising that one fails since it is used by a different network client. Several attempts to store a different static IP failed too. Same for DHCP.
I can choose here from several gateways - from 100 to 250 Mb/s. None works.
During the initial setup after the update I clicked off the privacy-touching entries - is this behaviour the fine now? 
What do you folks recommend? I am in the lucky position that we can receive TV also via satellite - and that works flawless. But then, every minute or so, a banner appears telling us that there is not Ethernet connectivity.
Not what Sony was once famous for, Mr. Morita, Sony's founder, rotates in his tomb, I guess.
Thanks in advance for any helpful advice.
Cheers from the shores of the Baltic Ocean!
nonetheless detaching power cam help resetting electronic components I'll make the hardcore complete factory reset later on - at the moment, the TV is in ordinary use. Never factory-reset a running system...
Stay tuned.
yep .. it will be like having bought a new tv 
PS: be aware that it takes time to reset, so don't worry if it seems blocked while doing it... it may be scary 
BTW where I should send the bill? 
Sony, department for de-railed firmware upgrades, customer care charity center... 