Whilst looking into possible alternatives to the canon gps unit I came across this fantastic little app / program.

Its still very early days but early testing has shown good results. The smart phone app at only £1.99 (Android App HERE) works very well and very easy to use.
Once setup its a simple case of letting it log your trip and then exporting the data via a bar code that you take a photo of.
Using the desktop software which is free to download from the website (HERE) it is then a simple case of telling the software where your photos are located. The desktop software then goes and inserts geotags into the meta-data of the files. I have used it so far on a short trip and it did indeed log my movements as best it could (only as well as the GPS could track me). It also inserted the geotags into the meta-data of my Canon 5D Mark III RAW files, Lightroom also picked them up during import and I was able to use the map function to view and make any small adjustments as needed.

For anyone looking for a very cheap and viable alternative to a dedicated GPS addon, take a look at this fantastic bit of software and help support its development.