Here's an interesting one. I had to replace my Lumia 800 because the Micro USB connector on the phone itself was going bad and constantly dropping USB connections. I mean if I breathed on the thing it would disconnect! Before it got exchanged (Yesterday) I did update to 7.8 on the faulty Lumia 800 on the 1st February at 18:00 GMT. I plugged it into Zune and as soon as it checked for an update, it was straight into the process all 3 updates without any problems.
Now on my replacement Lumia 800, it refuses to accept that there is any updates! I spent a good 45 mins doing to disconnect trick (various methods) and only managed to get it to cough up the NOKIA firmware update, but can't get Zune to cough up anymore updates, so I'm currently stuck on 7.10.8779. (The replacement unit came with Tango installed on it already)
I'm with EE (Orange UK). I guess I'm victim of the staggered update processes. I just find it interesting how one unit got the update and my replacement can't, the Model number is possibly different, everything else such as the SIM Card etc are all the same. It seems to be a carrier specific device still as it has Orange Branding and Apps pre-installed.
Need some 7.8 magic! I already hate the fact I can't shrink non-live tiles, massive space wasters! Start screen is ugly on 7.5 compared to 7.8!