Ok I've finally updated both our Mac's.
2013 13" rMBP 256GB/8GB = went perfectly no upgrade issues:
However I do have 1 post upgrade issue - connecting to SMB or CIFS servers works (win 2008r2) but if I drag a share to the sidebar it shows the server name instead of the share name and then doesnt work.
2012 i7 Mini 1.1GB DIY-Fusion/8GB = one major upgrade issue:
The installer refused to upgrade my Mini, said there was something wrong with my DIY Fusion drive (made with Mavericks). Disk Util couldnt repair the FD so I ended up having to use Terminal to break apart the Fusion drive. Once i'd done this Disk Utility happily re-combined them into a fusion drive (apparently if DU see's a Samsung SSD and Apple HDD, it assumes your mac has an OEM Fusion Drive and offers to "fix the Fusion Drive").
After that I was able to install El Capitan from my USB Key that i'd made earlier without dramas and then restore all my apps and stuff with Time Machine.
However I do have the same El Capitan issue - connecting to SMB or CIFS servers works (win 2008r2) but if I drag a share to the sidebar it shows the server name instead of the share name and then doesnt work.
I'm fairly ticked off about this but cant find anyone else with the same issue or any fixes (10.11.1 made no difference).