Really useful application which can help you getting from A to B using your Android device. I have been using it in several countries on my HTC Legend and it works quite fine.
Don't expect a software on par with the one on your Garmin or TomTom device - NavDroyd is definitely work-in-progress and especially entering an address can be troublesome sometimes.
Routing works fine and the voice directions are OK - especially if driving in an English speaking country as the accent for local names, e.g. streetnames, is quite heavy in other countries. (I'm using Pico TTS and have tried any other)
Right now there's no "recalculating route" feature. That means if you miss your turn, you have to make a U-turn and find your way back to the route. I expect this is a feature for the future.
It is easy to download maps for all parts of the world - however be aware that the maps for different regions have very different quality. You can check out the maps here: http://openstreetmaps.org
New versions of NavDroyd are released quite frequently. However, you need to pay full license fee again each time you want to upgrade the software - there's no discount for upgraders. Futhermore, once I had to upgrade in order to download/update my maps - I expect that they changed something on the map server during release of a new version of NavDroyd.
All in all it's a very good tool. I use the Google Navigation at home and NavDroyd while roaming.