We have been working with EFPS since last year Tower and Approach. Project delivery was poor and post op support almost non existant. There is no way so far to move the system on from the build we went live with except for a couple of patches for the worst problems.
There are a some fixes still required but when we finally get a control system running they should not be difficult to sort out [eventually!!]
The biggest problem people have is getting familiar with the system and some get it quicker than others. There is still a small group who struggle a bit when something " goes wrong" and while it is sometimes EFPS or lack of training, more often it's finger or memory trouble.
Having said all that I actually like EFPS. It is fairly easy to use and eventually most do get up to speed inputting the freecall VFRs. Would I go back to paper?...probably not. I think the benefits - a LOT less phone calls - outweigh the hassles [why did the strip do that?....not another bloody VFR who can't be bothered to file a FPL!!]