I'm really liking the Nuvi, especially with the larger, wider screen (I have older, tired eyes). Used a Streetpilot III for a long time and this unit is much better in all aspects, in my opinion.
Pretty much agree with all the current reviews on the unit, including the fact that it is a tad expensive. The manual is on CD, which isn't an issue because it's not really needed except for a couple thing (FM transmitter). I have yet to add an MP3 playlist, but a search gave pretty good instuctions for a how-to. The reall bonus is that everything worked out of the box including the pairing with my BB. That process took about 2 minutes (only have 100 in my contact list). Also, have a 1 GB aftermarket coming from a buy on Ebay. $30 compared to OEM at $90 plus. A friend uses the same aftermarket card and has no issues with it.
I also got the travel guide disk ($70) which, for my use, will be a bonus. The Nuvi 660 is dubbed the "Travel Assistant" and it is exactly that.