Hello all!
A while back, I created a spreadsheet that calculated the effective DPS multiplier from Accuracy. My intent was to allow a way for people to compare MIG and DEX from a damage-doing perspective. We're in the Backer Beta to provide feedback, and our feedback is only as useful as our information. Knowledge is power. Etc....
My spreadsheet was pretty well received. Sparked some good discussion about how the different attributes affect combat dps, and led to some new insights on my part from some errors pointed out by others. So I've taken your feedback into consideration and revamped the spreadsheet, adding new capability. There's now a master calculation sheet where you can vary any and all of these 17 variables:
Graze Damage
Crit Damage
MIG % Damage Bonus/Point
MIG % Damage @ 0
DEX Accuracy/point
Might
Dexterity
Base Accuracy (from class)
% Damage Bonus (abilities etc)
Bonus Accuracy (abilities etc)
Weapon Base MIN Damage
Weapon Base MAX Damage
Attack Speed (frames)
Recovery Time (frames)
Target Deflection
Target DT
DT Effectiveness
To calculate the resulting dps. Up to 20 different combinations are supported (and you can probably figure out how to add more if you want). My hope is that through the power of crowdsourcing, members of this community will discover new insights about the balance and tuning of PoE's combat and combat stats. Make informative graphs. See how a 25% increase in crit damage and an increase of the DEX Accuracy bonus to 1.5/level will solve all the balance problems!! (I just made that up, but you get the point). The more we know about the actual balance, the more valuable feedback we can give about balance changes. People are arguing elsewhere about really major mechanics that, while important to discuss, probably aren't going to change much. What will change, and what we have the chance to affect and improve, are the tuning changes. So please - use this spreadsheet! Find interesting relationships among the variables! Share your insights with the community.
So without further ado, here is the spreadsheet. Enjoy

Unfortunately I think there are some compatibility issues with Google Sheets - if anyone figures out how to make it work, let us know.
On to the second part of the post. This will be short, but I wanted to be sure and talk about it really quick. MIG vs DEX. There has been some debate as to if MIG or DEX actually increases your damage more. And as Azrael Ultima pointed out, the marginal benefit of one more point in MIG or DEX is directly dependent on the current value of the other variable. So here's a comparison chart. On the Y axis is the marginal % damage increase (% of BASE damage, mind you - so all %s are based on the same scale) and on the X axis is the current value of Accuracy minus Deflection.
As you can see, the math is pretty clear. If Accuracy minus Deflection is greater than 5, MIG is always going to increase your dps more. If Accuracy minus Deflection is less than 5, DEX will usually increase your dps more. Only exception is when Accuracy minus Deflection are between -5 and -20, where the dominating stat depends on your current value of MIG. So it would seem that if you want an optimal build, you don't want to completely dump either - but neither is completely un-viable or always better than the other one either. In particular, note that this basically means more accurate characters will do better against enemies with very high deflection, while more mighty characters will do better against enemies with very low deflection. Kind of makes sense. So (at least at first glance) it looks like these are pretty well balanced, from a dps standpoint at least (there are of course more factors to consider when comparing different stats than just dps).
So... that's what I've got for today. Take the spreadsheet - use it to answer "what if?" questions about game balance and tuning. Present insights with the community. Help PoE be the best game it can be.

PS - Here's the equations used. Might be slightly simplified from what is used in the spreadsheet (the DT usage I didn't even try because it's literally an entire sheet of the spreadsheet by itself), but the general idea is there.