1)page 11 line after equation 4. Insert "Galactic" 
between "local" and "interstellar".

*** Done

2)3rd line after equation 4. "quiescent" isn't really the right word
here. Later you refer to the diffuse interstellar radiation field
which is much better.

*** Fixed

3)After equation 4 or someplace else it would help to give a very
short physical motivation for the power law distribution in U. After
discussion with some other members of the team it is not entirely
clear what the distribution really is. Some people think it is the
drop in UV field as a function of depth into a cloud, but from
Bruce I thought it was either the distribution in flux incident on
clouds due to OB associations of various sizes distributed around a cloud 
or the combination of OB association sizes and distances from clouds.
But, if it is just the incident field then it seems to me that the method
will underestimate the dust mass depending on how much emission arises
from interior dust. A big section is not needed but a few pointers
I think would be helpful.

*** I tried to physically motivate the power law distribution in U in Section 5.5 of Dale et al. 2001:

"In the case of a diffuse medium where the heating intensity falls off primarily because of $r^{-2}$ dimming as one moves away from the heating source, one would write $dU/dr \propto - r^{-3}$.  For a uniform medium with $dM_{\rm d} \propto r^2 dr$, one gets $dM_{\rm d} \propto U^{-2.5}dU$.  In the other scenario, the case of a dense medium where the heating intensity is primarily attenuated by dust absorption, one would write $dU/dr \propto -U$ for a slab.  For a uniform medium, $dM_{\rm d} \propto dr$, so one gets $dM_{\rm d} \propto U^{-1} dU$.  The first case would be a reasonable approximation for the diffuse cirrus-like components of the interstellar medium, whereas the second case would be a good approximation for a photodissociation region near young stars.  Intermediate cases between the two given here should yield intermediate values for the exponent in the power law scaling."

Right now I've made a change to the text by simply pointing to the physical motivation described in Dale et al. (2001).  Do you think that is sufficient?  It seems beyond the scope of this paper to give a detailed motivation.

4)top of page 12, end of 1st paragraph. change "by mass by PAHs" to
"to total dust mass by PAHs"...Is that correct? q_pah is fraction
of tatal mass and not Carbon mass?

*** You are correct, and I've made the change.

5)equation 9. The PDR contribution in an earlier section of the
papers was for radiation fields greater than U_min rather than
100 U_min. You might consider making them the same.

*** I didn't notice that before!  I was following the definitions laid out in Draine & Li 2007 and Draine et al. 2007, but as you point out, there is an inconsistency.  I've removed "PDR" from the discussion surrounding Equation 9, but I still want to compute the U>100 fraction for consistency with the results published in Draine's SINGS paper.

6)page 16 bottom. Insert "modified" between "single" and "blackbody"

*** Done

7)Figure 3 caption. I would repeat the definitions given at the top
of page 12 for PDRs ( U > Umin) and diffuse componenents (U = U_min).

*** Done

8)Figures 4 and 5. Should these be log plots in Y or linear plots in Y?

*** I think in this case it could be argued either way.