Is there a excel-like 'trace dependence' feature in Turbo Tax? For example, I would like to trace where Real Estate Taxes impacted all resulting forms.

No - TurboTax does not have a "trace dependence" feature.

However, the CD/Download version of TurboTax contains a What-If feature where you can make changes in the return information and see the results.

The online version of TurboTax does not contain What-If worksheets.  However, two TurboTax Champs have provided alternatives in a response to another user:  How do I do What If scenarios in on-line version returns?

To access the What-If worksheets in TurboTax CD/Download please follow these steps:

1. Go into Forms Mode by clicking on the Forms icon in the top right of the blue bar. 
2. Click the Open Form icon at the top of the Forms in My Return list.
3. In the Search box type what-if  [remember the hyphen]
4. Double-click on the entry to open the form. 
5. Column 1 will populate from the current tax return.  [See screenshot below.]
6. You can start by marking the box Copy column 1 to column 2 and make changes in column 2.
7. For an explanation of the worksheet, right-click at the top of the form and select About What-If Worksheet.
8. A window will open with more information.
9. To return to the interview, click on the Step-By-Step icon in the top right of the blue bar.  

Thanks for the detailed answer. I wasn't aware there were differences. Is it possible to get the "talk to the CPA" feature if you use the desktop version? That was kind of a handy option.

Regards

Yes,  You can do this if you upgrade to LIVE.  This will allow you to have a one on one LIVE discussion with a credentialed agent.

Sorry no.  The Live expert help feature is not available in the Desktop program.

Only the Online versions have Live support.  See the Note at the bottom of this

https://ttlc.intuit.com/community/choosing-a-product/help/what-is-turbotax-live/00/27191