Well I got one today from my local Sony Centre and to be honest my thoughts are a bit mixed. (Bear in mind I already own a DVP-NS76H so my comments will often compare the two.)
Firstly the player's GUI and remote are the same as the 76H which is no bad thing. Playback is no different in terms of quality etc. compared to the 76H. 1080p makes no discernable difference on my PX70, (but I did have an eye test today so maybe I'll see something when I get my new prescription

) But overall more than happy with what I'm viewing.
Bad points: less connectivity - whereas the 76H had an optical and coxial digital output the 78H has only the coaxial. The player is also missing some user picture quality adjustments - BNR and MNR. (Almost certainly they are employed but just not adjustable by the user unlike the 76H.)
Multiregion hack: the player uses the same remote hack as the
76H. I did mine using a OneForAll remote from Argos.
Overall I'd have to say it's not as good the 76H - mainly due to lack of optical output and removal of user settings.
As an aside: the player has Bravia Theatre Sync so I tried using this feature with my Panasonic PX70 (Viera Link) and Samsung LE37R8 (Anynet+)
The Samsung was OK - pressing the play button on the TV remote switched the DVD on and changed the TV to the correct channel. Turning the TV off than also switched off the player. Unfortunately Anynet+ didn't allow any other control like pause, FF etc. (However the remote is programmable.)
The PX70 was poor. It recognised that there was a HDMI-CEC device present but said I had to use the devices remote! Reading the manual this seems a deliberate decision by Panasonic - basically Veira link will only work with Panasonic's own equipment. There seems little point in Panasonic using an industry standard then chosing to be incompatible with the rest of the industry.
Finally not all HDMI leads will work. My freeby SkyHD HDMI lead didn't support HDMI-CEC and neither was one of my QED leads - so check the leads compatibility.