The Nokia N900 comes with GPS and Ovi Maps. One thing that it does not come with is pre-loaded maps. What this means is that if you are out and about, and you need some navigation assistance, you have to connect to the internet and download the maps as required. While this will not be a problem with some people, it was with me. I disliked the fact that I needed to connect to the web for Ovi to find a satellite lock, and then to connect to the web to find my destination, then to connect to the web to download the maps of where I am, and where I want to be, and the places in the middle.
I found a page on the internet that discusses how to load Ovi Maps without needing to do it via Map Loader. This is particularly useful, as I don't use Windows or Mac OS X, and do not have the ability to install the PC Suite with Map Loader. If you are thinking of doing this yourself, do not concern yourself with the version numbers. The maps work with the current version of Ovi Maps installed on the N900.
Therefore, for a once off download (of around 90MB for all the maps of Australia), I am able to install maps, not on just my N900, but also on KittyKat's N900.
Lastly, I think the maps loaded on the N900 (after installing them from the website link) are a few years old. I was recently driving to Bacchas Marsh from Melbourne, and I noticed that I was driving on roads that did not exist in Ovi Maps. I wonder if I had downloaded the maps "on the fly" from the internet, if the maps would have reflected reality.