Don't build on external APIs

For one my older projects (agesearch) I needed access to search engine results which I used to 'calculate' a stratigraphic context of given keywords. The idea was to visit all pages the search engine returns and to use Ageparser to scan these pages for stratigraphic terms to estimate their chronostratigraphic context which should be representative also for the entire search phrase.

I started to use the YAHOO search API which nicely worked but after a while YAHOO decided to restrict free access and started to charge for the use of their API. So I switched to Google's Search API which also worked well and allowed me to access an even larger website index.
However, now also Google started to charge for API usage which again forced me to look for an alternative. So I came to Microsoft's BING API. This service also worked pretty good and now agesearch seems to work again. Microsoft still offers free access on this API but I could hardly believe to see that they recently placed it on their 'Windows Azure Marketplace' and offer several upgrade option.

So don't trust too much on external APIs even when offered by the big web elephants. Their strategy to introduce a new service for free and to restrict access and to charge for usage after a while truly can be a trap for your projects.