I agree with the above. Keep in mind that a lot of what you take for granted in a native app you'll have to build yourself. Scroll inertia, image carousels, determining a "flick" vs a tap, fixed tab bar - these are all something that haven't been 100% figured out. Yes, you can find solutions for each one, but try putting them all together and you quickly see the conflicts. Add in some caching of data and you'll learn that the HTML5 cache concept is different for each device.

I've tackled these issues personally, and at my company (iPad app). Keep in mind that your users will demand that your app at least feel native, if not the same UI controls. You think that you'll have the freedom to run on each platform, but in reality you'll be dealing with the quirks of each platform and that will set you back some dev time. Webkit is not 100% the same on each browser

What Phonegap gives you is a demarcation point to drop in your HTML code - and that's it. If you need API access for accelerometer, vibrate, etc then Phonegap can help. If your app is focused more on the user experience, then Phonegap cannot help you.

Do you really want to launch an app that will feel awkward on every platform, or just develop a native app for each major platform? That platform space isn't as large as you might think - iOS, Android, <pick your consumer markets third>

I'm a mobile product manager by day, my contact info is in my profile if you have any more questions.