The Microsoft Exchange Team introduced some serious fixes and additions in the Exchange Mailbox Role Calculator version 12.3. This version includes the following fixes since 7.8:

Additional functionality:

• Incorporated Megacycle adjustment formula changes mentioned in the Exchange Team blog Guidance Change- Calculating the Megacycles for Different Processor Configurations Formula;
• The calculator no longer requires you to enter in the adjusted megacycles per core for the server architecture you are deploying.  Instead, you simply need to obtain the SPECint2006 Rate Value for your server platform (consult www.spec.org);
• Added Megacycle Multiplication Factor – this works exactly like the IOPS Multiplication Feature does and was added as a result of RIM providing E2010 guidance on megacycle impact due to Blackberry devices;
• Active/Active user distribution scenarios;
• Added a new worksheet/section that documents the Activation Scenarios for DAG deployments;
• Added error reporting validation logic if HA solution results in greater than 16 servers in a DAG to not show any results, since the design is invalid;
• Dumpster size calculations have been optimized as calendar versioning storage has been reduced from 5.8% impact to 3% impact in SP1;

Bug fixes:

• Fixed Total Number of Databases / Server calculation to deal with scenario where lagged copies are deployed in both datacenters for Active/Active (Single DAG) scenario;
• Optimized Number of Active Databases after First PDC Server Formula removing redundant bad code and enabling single database scenario;
• Fixed Number of Required Mailbox Processor Cores for both PDC and SDC calculations to take into account the situation where the required megacycles to support the active load is less than the number of megacycles per core;
• Optimized Number of Required Mailbox Processor Cores for both PDC and SDC calculations to not assume all required cores would be 100% utilized by changing how rounding works in the formula;
• Fixed Number of Active Databases / PDC Server (After Second PDC Server Failure) formula to only report a value for the following scenarios: HA Only 3+ HA copies, 4+ servers; HA, Site Resilience, No activation block, 3+ total HA copies, 4+ total servers; HA, Site Resilience, activation block, 3+ PDC HA copies, 4+ PDC servers;
• Fixed standalone scenario to expose the total number of databases being deployed in the results section when there are multiple servers;
• Fixed Number of Active database calculations (after first PDC server failure) to take into account activation block;
• Fixed the Number of active databases during normal runtime formula to round up;
• Various formatting and text cleanup across all sections;
• Fixed data error validation statement for IOPS and Megacycle Multiplication Factors to specify the supported value must be 1 or greater.

Consult the changeblog here, including information on the new user distribution models (single/multiple DAGs). You can download the calculator here. Updated usage instructions can be found here.