My first web-based iPhone application - how to do it right?

I've built my first web-based iPhone app and I have some performance issues that I needs to be resolved. I want to verify that I'm doing it right, so your feedback is really appreciated... :-)

sending data to a webserver with NSMutableURLRequest

I am creating an iOS app that needs to send a post to a php script. the php script then takes these values and updates an xml file. I can't for the life of me figure out why this wouldn't work... Also how could I test to see whether or not the php script is actually receiving data? Here is my objective-c code: