So, I bought the Tom Tom application for the iPhone a few days ago, intending to use it in the car. On a whim last night, I fired it up and asked it to take me home while riding. I started playing music on it, put the earbuds in, put on my helmet, put the iPhone in my pocket and zoomed off on the bike. I was pleasantly surprised; it works quite well, softening the music to give you directions. It doesn't chatter incessently at you; but rather gives you directions only when you need them. It seemed to get a signal just fine in my pocket, and didn't skip a beat. It chews the power a fair bit so it might be a good idea to get a charging cable for the bike if you intend to use it for a long ride. As a full sized GPS replacement, I think it's a pretty good app, and the convenience of having it all in a single device is a huge win in my book. If you already have an iPhone, don't currently use a GPS unit on your bike but are thinking about getting one, check out the iPhone Tom Tom application. Its currently got $20 off on the price, so its a good deal, I think.