Don't forget the code needed for Dropbox in your didFinishLaunchingWithOptions method. You can likely copy & paste the handleOpenURL function to your AppDelegate.m

AppDelegate.m

/**
 * This is main kick off after the app inits, the views and Settings are setup here. (preferred - iOS4 and up)
 */
- (BOOL) application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions
{        

// there will be more code in this method for your PhoneGap application

// code needed for Dropbox - Do not forget this
    DBSession* dbSession =
    [[[DBSession alloc]
      initWithAppKey:@"Your-App-Key-Here"
      appSecret:@"Your-App-Secret-Here"
      root:kDBRootAppFolder] // either kDBRootAppFolder or kDBRootDropbox
     autorelease];
    [DBSession setSharedSession:dbSession];
// end of code needed for Dropbox

}

// this below happens while we are running in the background, or from within our own app
- (BOOL) application:(UIApplication*)application handleOpenURL:(NSURL*)url 
{
    if (!url) { 
        return NO; 
    }
    
    // calls into javascript global function 'handleOpenURL'
    NSString* jsString = [NSString stringWithFormat:@"handleOpenURL(\"%@\");", url];
    [self.detailViewController.webView stringByEvaluatingJavaScriptFromString:jsString];
    
    // all plugins will get the notification, and their handlers will be called 
    [[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:CDVPluginHandleOpenURLNotification object:url]];
    
    // code below needed for Dropbox
    if ([[DBSession sharedSession] handleOpenURL:url]) {
        if ([[DBSession sharedSession] isLinked]) {
            NSLog(@"App linked successfully with Dropbox !");
            // At this point you can start making API calls
            NSString * jsCallBack = [NSString stringWithFormat:@"authDropboxFinished();"];
            [self.detailViewController.webView stringByEvaluatingJavaScriptFromString:jsCallBack];
            // user linked with Dropbox, call authDropboxFinished() in dropbox.js JavaScript
        } else { // else user didn't successfully link with Dropbox
	    NSLog(@"User didn't finish the Dropbox link process");
        }
        //return YES;
    }
    // end of code needed for Dropbox
    
    return YES;
}