Voice search is improving all the time, and Google brings the best we've seen to date. Its stellar iPhone app uses the accelerometer to activate search. When you hear a beep after lifting the phone to your ear, start speaking your search term. The accuracy of the listening software combined with the MyLocation feature brings (mostly) spot-on search results that are localized to your whereabouts. As with versions of the Google Mobile App on other mobile platforms, this one also includes a tab of shortcuts to other Google services, including Talk, Reader, News, and Photos (Picasa Web).
While the search app performs nearly error-free, some people are disappointed that Google Mobile App doesn't hook into your iPhone's address book to voice dial your contacts. Apple doesn't currently allow third-party apps that sort of access.
In addition to voice search, Google has integrated Goggles, its stab at visual searching. Tapping the camera button initiates the shooter. It works best when aimed at logos, landmarks, books and DVDs, business cards and businesses, labels, and barcodes. It usually fails when pointed at people, food items, plants, and animals, and Google will caution as much. While Goggles is still an in-development Labs app, and fairly bare-bones on the iPhone, it's nice to see a version here, and not just one on Android phones.
The voice, text, and now visual search features combined make Google's mobile app a go-to search tool on iPhone.