Depends on the way you construct Q. For half reaction
Q = [Oxidised]/[Reduced]
and Nernst equation gets form
E = E0 + RT/nF ln Q
Same goes for more complicated reactions, like
MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O
Just put oxidized form in numerator:
Q = [MnO4-][H+]8/[Mn2+]
(note that water concentration is taken from the Q, as it is assumed to be constant and not changing, thus it is moved to E0)
It is just a matter of convention used, you may as well use minus and reverse Q exchanging numerator and denominator.
Looks like I was not precise in my previous post, hopefully it is cleared now.