I've spent the last weekend working on the Guatemala GPR data with Dean Goodman's fantastic "GPR Slice" software (www.gpr-survey.com). There are aspects about the software that derive from its PowerBasic origin and "command line" type interface, but it the best thing around for generating 2D horizontal slices for multiple time-transect data. The results are stunning and the control one has over all of the steps of processing is spectacular. It takes a bit of training to use, but once mastered you have one of the ultimate tools for geophysical research in the archaeological record. One of the recent projects I've worked on is the re-analysis of the VA11 data from El Baul (from 2007 and 2006). You can see the results by clicking on the figure on the right (one annoying problem - the .jpg output always includes all possible grids to determine length when the set of slices might only be a few).
I've also processed a chunk of the VA11 data from 2006. This correspondences neatly with the 2007 data. One can see the sharp beginning of the causeway as it angles north. This image is also on the right (but you will need to click on it to really see anything).
One bonus aspect of working with Dean Goodman is that he is constantly updating his software and is always willing to entertain notions of new features, new tools, etc. As a result, the more one works with GPR Slice, the more useful it becomes.