It's not particularly interesting to be out of sync with the rest of the world, you always are and messages to/from external entities are even more so constantly. When it is interesting is when the thing you are doing is a function of time e.g. GPS or locked-step systems spanning geographic regions or so on. In almost all of those cases you're probably well used to dealing with time problems that are a bigger pain than a leap second. For those that aren't hiding the leap second and being off by slightly more than usual for a bit is probably better than hoping everyone can be prepared to suddenly care a lot about handling time oddities for one second every year (or century as you propose).