I'm a current iPhone 3G user who will be switching to the Pre on release day. My main reason for the switch is AT&T, and their lack of a 3G signal when their coverage map says I'm in the middle of 3G coverage. Oh, and the countless dropped calls too. Dog Sprint all you want, their network at least where I live is one of the best in my opinion. Not to mention I get 450 minutes with unlimited text, data, navigation, MMS, and nights that start at 7pm for a little less than $55 a month.
The Pre is simply the first WebOS phone being released, there are rumors of two more slated for release before the end of the year in two different form factors. The Palm "Pixie" will be released on Sprint and AT&T this fall.
Look you insecure fanboys, nothing will kill the iPhone, nothing. However nothing will kill RIM, nothing will kill WM devices, and nothing will kill Symbian. They're still around and doing very great two almost three years after the iPhone's release. With as great as the iPhone is, they weren't able to put a single phone platform out of business. Palm never touted WebOS as an iPhone killer, they are simply going after the fast growing market of smart phone users.