For anyone that uses an iPhone for business, it is a very big deal. It will fall under the saying "you don't know what your missing until it's gone". Most people using iPhones probably don't even think about it. They will have a harsh wake up call when they realize talking on the phone while using the data for anything from navigation, looking up info, emailing etc... If you think "multitasking" is a big deal, go try using a smartphone that doesn't allow voice and data at the same time.
I for one never thought twice about it, decided to try put try the Evo before committing to another contract on ATT, lots of great features on the Evo, biggest missing item voice and data bar none.