There's been a very positive response to this site's Mashup Tag Cloud and a couple readers had a good suggestion: can I see the distribution of mashups across APIs in order to see which is used most/least? And now you can. Go to that /cloud page and click on 'View by APIs' and you'll get a tag cloud sized by API usage. While by no means a scientific sampling (ex: eBay and Amazon have many more examples than captured here so far), it gives a good summary of this subset. Within this collection, one web service conspicuously sticks out. Is that the one most widely used overall? Probably, but the space is changing so rapidly that that's only true for the moment.