I've purchased the very new DSLR Remote Professional Edition and made a short test with my Canon 40D and MacBook Pro. The app works as advertised and crashed once in 30 min (okay it's version 1.0).
AppShopper (Professional Edition)
iTunes:
Professional Edition ($9.99 7.99)
Lite Edition ($1.99 1.59)
Manufacturer's product info
DSLR Remote Professional Edition is the next-generation cable release for your Canon EOS© DSLR camera. Just connect your camera to a WiFi network and you can instantly adjust its settings, fire the shutter, review images, even get a live viewfinder preview using your Apple iPhone or iPod Touch. DSLR remote is a must have for remote shooting applications like high or low angles, self-portraits and children. With its advanced timers it can make remote monitoring a snap too. All you need is your Canon DSLR and a WiFi enabled computer to start shooting now.
Remotely fire your Canon DSLR over any WiFi network
Remotely control the camera settings like shutter-speed, aperture, white-balance, etc.
See the images you have taken right on your iPhone or iPod Touch
Look through your cameras viewfinder remotely with Live Preview
Built-in Intervalometer for advanced timer shooting
Great for difficult camera angles where it is difficult to see through the viewfinder
Use it for self-portraits, you can compose and review your shot without having to move to the camera
Use it for remote firing at weddings and sporting events