I have a Garmin xTrek - waterproof/rugged, runs for hours on AA's with topography maps. Works very well when you're way out, such as when we were in Elk Island National Park last year. It has a logging function, and also one to show you the way back.... we needed that one in Elk Island. All the trails looked exactly the same.
For general use tho, the iPhone works great. I have "iBirds plus" loaded - only $20-, which is like a Sibley's in my pocket. I can also check Ontbirds and site guides via the web browser while I'm out. Google maps is okay as a GPS application, you can add pins as you go along, but it doesn't have the level of detail for trails like the Garmin. Then again, the Garmin topo maps for Canada cost me over $100- and the xTrek was about $300-.
I typically use my car mounted GPS for getting to locations, but most of the time, the info available in birding reports is only good enough to get to the general area.
