Depends on the battery I guess, but I think most batteries will overheat if you try to charge them too fast. It might decrease their longevity too.
Also of interest is this article: Electric vehicle charging times will depend on both the charging station and the car.
Basically, it appears that the on-board charger limits the charging speed to protect the battery. The Leaf and the Volt are restricted to low-speed charging (3.3KW charger), which is about half of what a standard dryer outlet can provide. Future models, at least of the Leaf, are expected to have a 6.6KW charger. However, the Leaf does have the ability to accept DC voltage (like that available from the Blink stations), which skips the charger and goes straight to the battery.