Yep, used it at both DLR and WDW. Although we did not strictly follow any RideMax itineraries on our first WDW trip, I did use it to "test drive" how much it was reasonable to experience at different parks. It was especially helpful to me at MK and Epcot.
I already have a good idea of how lines build at DLR, but did not have that for the WDW parks. Playing around with RideMax helped me gain an understanding of this.
If you are someone who wants to experience certain rides and does not want to have to think about what to do first, RideMax is especially helpful.
See my RideMax review here:
"RideMax Critique Plus Conventional and Unconventional Usage on August 1-4 Trip"
http://www.disboards.com/showthread.php?t=885134