In 1.9pre, you could enchant items multiple times, but in MC 1.0.0, nothing even comes up when I put an enchanted item on an enchantment table. Has this been removed? Is it a bug? I am in SMP, if that's important.
Items could never be enchanted multiple times.
It was (and still is!), however, possible to get multiple enchantments at once (as long as you spend enough levels).