I tried Navit yesterday and found that, while it did display my location correctly on the OSM map I downloaded (a 30mb map .bin from OSM for my area), it really hogged the CPU and was very slow responding. I grabbed the .deb from Maemo garage, which was built using an older version of Navit than the wiki shows as the latest. Before I'd loaded the map, it was very responsive and seemed rather promising.

I was slightly put off that I could only get the GPS to display in Navit when I had the GPS location app running - if I closed that, the tablet (and Navit) lost connection to my GPS.

I'll keep my eye on this project, it has a lot of potential.