Yeah its pretty crappy compared to alot of after market units. Compared to Acura and even Lexus it is poo.
Compared to Audi and even Mercedes, its more or less the same level.

My biggest gripe actually is the lockout. If it didnt have the lockout, it would be so much nicer. My wife works it mostly on long trips and alot of things like re-routing would be nice if it could be done on the fly. Iit has a seat pressure sensor on the passenger side, it should know better than to lock it out.

If i were to do it again, i think i would still get the oem nav. Yeah it sucks compared to acura, but the built in factor is a huge conveniece when compared to the after market units.

Once the destination is in the unit, it does work well. So the fact that i dont have to lug anything in and out of the car, i still would recomend it over after market.

FWIW the 06 nav uses the same menus as the M, and the screen is sharper than even the acura unit in my friend's mdx. (A big improvement over the 05 g35 imho)
The popup factor, in addition to being VERY cool, is very stealthy, making my car look a little less desirable on the streets of ny. Popup also keeps the screen very high and visible on the dash, better than most any other oem unit ive seen which almost forces you to look down. Its also easy on and off, very handy if yer on a long stretch of road and dont need the map, but want to keep the destination set.

So its over priced, feature lacking, but the oem unit does work pretty well once yer used to it. The convenience factor of having it built in would make me choose it again.