My mouse broke; I tried to install 8.1 beta on that machine, anyway.
It accepted the 'no mouse' option, carried on, to the summary alert box, then
declined to accept it further; I had to lie about having a serial mouse
(which didn't exist) in order to continue. Several of the mouse choices don't
work for me, possibly due to non-existence of mouse :), but I did expect 'no
mouse' to actually be allowed. I think it's that final dialogue where you get
the option to review your choices that wants attention.
Additionally, having got it installed, you don't appear to get an option on
'start X by default' and the Shutdown button on the Login screen no longer
has a 'return to shell' option - Damn! I liked that option, and needed it
today. [Well, OK, wanted not needed...]
Mark