Google is starting to add advertisements to Google Local, which now shows sponsored locations on select searches. For example, if you search for hotels in New York, you’ll see four pushpins denoting hotels that paid to be there, along with some listings for the hotels in the search results, two at the top, two at the bottom.
It's interesting to notice that sponsored listings don't include options like reviews or driving directions.
For most searches, though, you will see simple AdWords ads, not related to the map, but related to your query.