Transforming FFT to Detect Baud Rate
As noted in the following link, baud rate is estimated from "the spectrum of the signal after nonlinear processing."  In their case, as noted in the first three sentences of the section entitled "Proposed Spectral Approach for Bit Time Estimation" - p. 916), the nonlinear processing is the first derivative followed by an absolute value operation:

http://www.iasj.net/iasj?func=fulltext&amp;aId=51991

Others have proposed/analyzed estimation using different nonlinear operations, such as squaring of the signal or using higher derivatives.  Obtaining the references for the above paper and doing a thorough search would be a good place to start to learn more.