One of the primary issues facing map mashup developers isn't a technical one but a business one: how to make money from their mashups. Often you'll see Google AdSense ads ringing a mashup as basic strategy for generating a bit of revenue. This problem is one that IDELIX Software, a veteran Canadian developer of visualization tools, is aiming to solve with their new product Lat49.
Overall the problems they want to solve for mashup developers in this situation are: screen real estate -- maps are often forced to be smaller in order to make room for ads; ad relevancy -- the limited amount of text on map-centric page reduces the text usually used to drive ad relevancy algorithms; and lack of ad refreshes -- due to Ajax-driven sites that lack the old page reload model.
On the advertisers side, they 'lease' space by the 'tile' of land. Ads can be specified at four different zoom levels ranging from Local, Neighborhood, Urban, to Brand. Pricing and revenue sharing models are being ironed-out now. I spoke with their team yesterday and they're looking for publishers and advertisers to take part in their current alpha testing and you get their contact information from their site.