Well, [itex]\hbar[/itex] is just [itex]h/2\pi[/itex], so that formula, which is the instantaneous power output of a simple non-rotating black hole of mass M, is also written

[tex]\frac{h c^6}{30720 \pi^2 G^2} M^{-2}[/tex]

Note that the qualification "Planck Units" makes no sense. The number is dimensionless. It will apply for any set of units. What changes with the units are the values for G, h and c. The additional dimensionless factor, if we use h rather than hbar, is about 303194.2472

Also, what I found interesting about that formula was the index of c. c is generally pretty large, unless you pick units to make it 1. And this raises it to the sixth power! Off the top of my head I cannot think of another natural physical relation which raises something to fixed powers more than 6.

The number of string vacua is estimated to be something like 10^1000 or bigger. Even though it is not calculated exactly, it is calculated from first principles and corresponds to the number of different topologies of Calabi-Yau spaces describing possible compactifications of the additional dimensions in string theory.

Or should we only count numbers in 3+1 dimensional physics?

Here is my turn.
Lets say we have a black hole of mass M
We wait until it evaporates completely.
So the original BH it is replaced with a sphere of hawking radiation
That Hawking radiation occupies much more space than before.

Just to repeat the precision done above: a dimensionless number is dimensionless, it does not relate to the units. It is usually a quotient of two measures with the same dimensions, for instance the fine structure is a quotient of two angular momenta.

Unh... Here goes: well-nigh every (super)string compactification thus far constructed ends up having at least one continuous parameter, and so the "number" of such particular compactifications is uncountable. Moreover, typical Calabi-Yau compactifications ever constructed have many (tens, hundreds, some even a thousand or so) continuous parameters. And, that's not all: Miles Reid (a mathematician of considerable repute in the field) is on record having conjectured that there may well be possible to construct indefinite sequences of different "topological types" of Calabi-Yau manifolds, each one suc manifold equipped with an ever-larger-dimensional parameter space.

In turn, the physics of such compactifications imposes a certain quantization effect (discovered as best as I know by Joe Polchinski of the Kavli Institute, Santa Barbara), whereby in this vast continuum of Calabi-Yau (and related) compactifications, only a "sufficiently dense" subset represents completely consistent models. This quantized subset is what is sometimes guestimated as 10^500 (give or take a Googol ), and is called "discretuum".