TUAW writes Apple filed a patent application for a solution that would turn an iPhone or iPod into a fully-fledged bike computer system:
Patently Apple has just discovered a 2009 Apple patent which would turn an iPhone or iPod into the bike computer of my dreams. The patent shows an iPod (amusingly, the third-gen "fat nano") standing in for a bike computer and accepting the same sort of data as my current Polar computer, like speed, cadence, heart rate, and so on. But the patent also shows much more interesting features like turn-by-turn GPS, gear settings, and sharing options that would allow cyclists to communicate with one another in ways not possible with the current crop of bike computers.
It's the sharing options that are the most innovative, and they basically come across as Nike+ for bikes. With routes mapped via GPS and riding characteristics recorded via the bike's sensors, this iPod/bike pairing could allow riders to share realtime data on their rides, assign ratings to trails, and even form riding groups based on compatible fitness levels.