A couple of those macros don't work.
If you try to cast a spell that has a gcd it will stop trying to cast anything after that (except spells off the gcd), even if the spell is on cooldown. So take the "super fun midair death" macro:
#show Frost Nova
/dismount
/cast Frost Nova
/cast [mod:shift] Slow Fall

That will actually kill you too since you won't be able to cast slow fall with it (not to mention that slow fall is now a targeted ability). Try using this instead:
#showtooltip
/dismount
/cast [mod:shift,@player] Slow Fall; Frost Nova

And [flying] only relates to yourself (and only when your actually on a flying mount too, falling doesn't count as flying), so this macro:
#show Remove Curse
/cast [target=mouseover,noflying,nomounted,nodead,help] Remove Curse [target=mouseover,noflying,nomounted,nodead,harm] Counterspell; [flying,combat] Slow Fall

Will *not* cast Slow Fall on "an ally who is midair", it will simply cast slow fall on your current target (not mouseover) if you yourself is on a flying mount and off the ground (and in combat), thus dismounting you in midair if you allow spellcasts to dismount you when flying.