A few comments:
I agree with burningjoe and iphonenut, who thought the iPhone could compete with a core duo machine?
But more importantly, the fact that a JavaScript code runs slower than native code is not a valid argument against web apps for a few reason. First, the web apps that Apple is pushing are AJAX-based applications. In these applications most of the work is done on the server and the results are sent to the iPhone to be displayed. Therefore, JavaScript is needed for a small fraction of the processing requirements of the application. Second, a large number of applications that are needed do not require a lot of speed and will function just fine as a web apps. If anything, your bottleneck is probably going to be the data speed and not JavaScript. For things like graphics-heavy games, for example, you'll need all the processing power you can get and native applications are a must.
I am actually quite impressed by some well-programmed applications for the iphone, for example Scenario Pocker:
http://iphone.scenario.com. It is hard to tell that this is a web app!
I'm not saying that web apps can do it all for the iPhone, but I'm saying that JavaScript speed is not a valid argument against them.