The sponsor had trouble navigating slides quickly when questions arose. I also find that composing PowerPoint slides takes more time than using LaTeX, especially when inserting new elements and moving bullet items at the bottom of one slide to the top of another slide. Equations are a real problem with PowerPoint. Someone mentioned to me that one department in one of the branches of the US military has forbidden PowerPoint from being used, because of productivity loss and overuse of frills. The biggest single problem with PowerPoint is that it offers temptations to the composer to add non-substantive features to the presentation.
Navigation is simple, fast, and slides look scientific.
I have not tested wmf created with the new wmf.graph function in Splus 6.0 beta. Usually all the editing that we need to do for imported wmf files is re-sizing. But just that will distort the graph, especially if dotted or dashed lines are used, and in some cases, if heavy lines are used. This is an excellent issue raised to me by Jim Pratt. Also, we commonly update graphs when new or corrected data arrive.