With OpenLayers, you can even customize the behavior of your map, because it is designed as a JS library rather than a proprietary web API. Also, the clean separation of presentation (map client) and data source (any map server speaking WMS/WFS/whatever) enables you to combine any map data from any sources. Thus, handy overlays are possible without relying on the mercy and the pre-defined possibilities of Google.
Then you can style them, and design a map, using vector drawing software like Inkscape.
Note that his requires writing support (WFS-T or similar) on server side. However, the typical map servers such as GeoServer and Deegree all do support WFS-T.
Nice service, but given that HN is for startups (i.e. commercial entities) these terms make it kind of useless to most of us don't they?
I mean it's based on OpenStreetMap.
Check out the actual site http://www.cloudmade.com/
It's not like these two services are 100% identical. Cloudmade have a bunch of nice tools to style the maps with.
I'm not sure what you mean by your second point, the Maps API has very flexible overlay and projection capabilities.
Styling is encompassed under design (waaaay not different).