We're currently #46 in the Top Paid apps for the Navigation category, so I think it's safe to say that the influence has been substantial. We won't get to see actual sales numbers until tomorrow morning.
Google uses different algorithms for walking & biking. For example, you can walk in either direction on a one-way street, but you can only bike in one direction.
The bike directions prioritize streets with bike lanes and low traffic bike boulevards. With walking, really any street with a side walk will do.
I still remembered a decent amount of C from high school & college (I'm just old enough to have snuck through before Java took over CS). I brushed up on the ol' K&R and then read about 2/3rds of O'Reilly's Programming iOS 4 book.
Apple's documentation and sample code is excellent, and really nicely integrated into XCode. Once iOS 5 came out, I learned almost exclusively from there. Of course, Stack Overflow is great for very specific gotchas and questions.
I did all the work on a MacBook Pro, with glossy screen, usually plugged in to a 27" Apple display (also glossy). The gloss doesn't cause me any problems unless I sit in very bright sunlight, but all things equal, I would prefer matte. Xcode is a bit of a pig, so it definitely does best on a big display.
We're a team of 2. I do all the development. All the work was done in-house... no outsourcing. The app, icon, and website were all us.
It took 3 months to get to version 1.0. We worked on it part time, nights and weekends. There were some big gaps as life and work got in the way. It was my first iOS development experience, and I had only dabbled in Objective-C previously, so most of that time was getting up to speed with the language and framework. I primarily work in Ruby.
There are no real ongoing costs. The website is completely static, so hosting is negligible. We use Google's local search and directions APIs. Both of them are free at our usage levels.
It cost $99 for the Apple developer license. That's all the capital all we invested. The rest of it was just time.