wbill76,
I have heard of numerous problems associated with not letting enamel paints cure completely. For armor modelers, and a lesser extent others, the biggest problem I read about are pre-wash coats of Future being placed over uncured enamels. The solvents in the enamel are deprived of the air they need to evaporate completely. I've read about these solvents discoloring or breaking down the Future coats, warping small or thin parts over time, or in extreme cases, even causing the underlying enamel to slowly "slump" on the sides of models.
The other problem is caused in even the most apparently dry (but uncured) enamels when subsequent washes or paints are applied that have compatible solvents to the original paint. If an enamel in completely cured, it can literally be washed in the same solvent as was in the original paint (but I wouldn't recommend it - obviously). This is because the paint vehicle has been allowed to actually change on a molecular level into something harder than before. However, with uncured enamels, even a couple of drops of solvent can cause the curing process to stop and the paint vehicle to once again break down.
Granted, most of these are probably severe cases, but my thoughts are these. If the manufacturer recommends 24 - 48 hours for the paint to cure (or longer in some cases), why in the world would we as modelers jeopardize the look of a $15, $30, or even $100 model because of nothing more than being impatient. It's just not worth the risk with the amount of money we put into today's models.
Enjoy your modeling...