It looked like the latest update killed my N810 as well. It would just sit at the initial boot screen and do nothing. The scary part was that I could not get it into USB mode to reflash.

After leaving it at the boot screen for a few minutes (maybe 5 or so) it suddenly completed booting. Now there are periodic slow down (one minute to complete "sudo gainroot") but things seem to be working again.

I had left my tablet in "no-lifeguard-reset" mode since flashing, if that is relevant.