I've been using Ovi Maps 3.0 (the offline application) on my N82 extensively during the last 2 weeks while on holiday in Croatia (Great country!).

Ovi Maps was a very positive experience. It saved me hours while looking for my hotels (I switched location every 1-3 days) and while walking through smaller cities and villages where I didn't have a city map with me.
I'll be VERY glad if the app finds it way to the N900, hopefully bringing the same map data and licencing model with it.

Advantages:

• Good maps for many countries freely available for download to the device (offline usage, no data cost while in a foreign country)
• Easy interface to search for addresses and POI
• Impressive turn-by-turn guidance, works really well
• Good integration with Ovi Maps online (didn't use that, but sounds very interesting).
• Very interesting licencing model. I only need navigation sporadically, glad that I don't have to pay full price for a year but can buy daily licences. WISH: Let users buy a "pack" of turn-by-turn guides, e.g. 20 usages for 20 EUR. (The amount of work to get a daily licence is bigger than the amount of work to find a location with Ovi Maps without turnbyturn :-). This would also save one from having to use an online connection while abroad if one needs a licence - instead one could buy the licence "at home" and use it whenever wherever needed.

Negative points:

• POI data quality average, many POI missing or incomplete (ATM, Hotels)
• Minor: Auto-rotating maps are a bit too automatic, I had problems to keep it fixed north. Instead, Ovi Maps too often insisted on rotating the map to the currently traveling direction (might be a user-related problem :-)

One funny note: The maps include information about the speed limit on certain roads. The app can be configured to warn if one goes over that limit. Now I was traveling by public transport in a large bus and using Ovi Maps to keep track of the route and location (so as to know where I was, where I had to go off the bus etc.). So while the bus driver was racing along the coast, my N82 suddenly and loudly yelled "watch the speed limit!"