The software is a large, 970 MB download, but that means everything is on your phone, so it doesn't need to get data from the cellular system. I consider this a big plus. The cost of the system includes software updates and map updates until December, 2010.
I found a lot to like with the iGo software, with one big caveat so stick with me until the end of the review. From a feature standpoint, the iGo is quite complete. Unlike the competition I've reviewed, (AT&T Navigator, Navigon, G-Maps) the iGo lets you select from multiple voices, male and female. The voices are clear and understandable. While navigating to a destination, there is a soft 'gong' before a voice announcement, which helps me focus. iGo uses the Navteq database, which is also found on the Navigon. Like the Navigon, it does not use text to speech, so you will get "turn left in 100 feet" instead of 'turn left at Mission Street".
Address input is easy, but unlike the Navigon, it does not allow you to use your existing iPhone contacts. It does have auto complete, which makes the process pretty fast. The developers say contact input is coming in the next update.
The maps are easy to read. The display can be set to go to night view automatically, something Navigon lacks. The display, like all the nav apps I have tried, lags a bit behind real time, but not distressingly so. It's unlikely the iPhone hardware and nav software will ever run as fast as a dedicated GPS unit, but I think all the apps I've tried have been more than adequate to the task.