I started using PlaceTagger for iOS and Mac for geotagging my pictures from Nikon D90. There is an original Nikon GPS unit but is costs too much and you must mount it on the flash mount to use it. Not practical at all.
It is sold separate for 4,5 EUR iOS and Mac respectively but I could not find a better app for iOS with a cool design. Yes, I know, functions are more important but I saw some alternatives and was not satisfied with their design.
PlaceTagger for iOS uses iCloud to sync the geolocation data with the Mac app but for some reason PlaceTagger for Mac will not read my data from iCloud. I do not know if it is iCloud’s or PlaceTagger’s fault but I export now my data from the iOS app over email and add the .gpx files into PlaceTagger on the Mac. It works nice.
Anyway, PlaceTagger is a nice iOS app that has a Mac client to make geolocation tagging more simple.
One new feature would be adding support for Dropbox since iCloud is not a reliable service for now. You would only authorise both apps for using Dropbox and the Mac app could read the geolocation data stored on Dropbox. Simple. No need for emailing (yes, emailing is annoying for me but that is the only way I can use the data for now).