Couple of downsides so far....
There are 24 downloads showing in the store with 'Attention required. Tap here.'. I take it these are apps that are no longer published so I'm going to have to compare the app lists on my 920 and 1020 to see what exactly is missing and find suitable replacements.
Also, my high res photos are no longer available in the gallery. Before flashing, I backed up my photos and copied them all back to the phone after flashing but there's no option to view images in ProCam anymore which is a huge disappointment.
I'm also tying to work out which accent colour looks best with the yellow 1020. Not a problem as such, it's down to personal preference. Yellow seems to go well but some tiles, especially email don't read too well with white text. Amber seems a little dull. The red contrasts well with the yellow body and works well with the black display but I'm not a huge fan of red....