Continued use of GPS running in the background can dramatically decrease battery life.
For all iPhone users myLog is the easiest, most affordable, complete, save and fast tool to compile a log book - or as you say today: a blog about your voyage. myLog utilizes the iPhone sensors to compile your GPS voyage log book very easily.
myLog works without a network. A data connection is established only to publish the voyage (this may incur costs, depending on your contract), with myLog you can create new waypoints and pictures by shake.
The application has a power saving mode and creates waypoints automatically if desired (e.g. every 5 minutes).
Of course, myLog works just as well for hiking, biking, in a car or on a train.