When you're trying to pinpoint locations that aren't street addresses, or show large area overlays, all that extraneous information is distracting, and works against usability.
It'll also be great to finally be able to show a map that's not jarringly obviously from a third party provider. (I'm totally cool with the small google logo/copyrights, but the color scheme just screams 'outside embed').
I realize that I'm in the minority about this when I look around and see most of my competitors customizing the look of their markers, etc, but I think they just make it worse most of the time. This is granting much more power in that department.
I'm happy for the power, I just vehemently disagree that this is going to make map mashups much better overall.
I don't think "outside embed" is a bad thing when viewed from the eyes of the user - it's comforting familiarity for many. Making it seem custom is just an ego trip.
If you want complete control over your maps, check out Tile Drawer - http://tiledrawer.com/ - it lets you define your own map styles using a Cascadenik stylesheet, then run your own EC2 instance that will render and serve custom tiles for a specific area using those custom styles (and OpenStreetMap data).
Back in the day, companies were getting tens of millions in funding to build apps where users could place pins on a map. That says a lot about the hype surrounding it, since that's essentially the app you got when you pasted their sample code into your IDE and hooked it up to a database.
Today, it's just expected that any application you build will have a GMaps implementation somewhere in it, but it's just old-hat. I actually run one of those GMaps-based startups from back in the day, and I haven't kept up on the latest API changes for years.