Why is Google maps (the built-in app) so slow on the iPhone 4?
From a MacRumors.com forum post:


  My problem: Typing on the Google Maps app was very slow, independent of network connection.
  
  My solution: Apparently there are issues with the GPS multitasking. I went to Settings > General > Location Services. Notice you can toggle the GPS for each app. Apps using the GPS have a purple arrow next to the ON/OFF switch. I turned location services off for every other app with the purple arrow. I went back to the Google Maps application and everything worked well.
  
  This might not work for everyone but it worked for me.