Citi financial analyst Mark Mahaney put out a research note this morning that discussed the new comScore search market share data. Here's an interesting bit about mobile from the note:

comScore doesn’t include Mobile Search results, which are likely growing very rapidly for GOOG — perhaps triple-digit Y/Y growth % and now accounting for almost 10% of total GOOG queries.

Let's assume that figure is accurate -- comScore and Nielsen don't have good figures about mobile queries -- what would that 10% mean in concrete terms? Ten percent of 10,292,000,000 monthly queries is 1,292,000,000 or more than 1 billion monthly search queries coming from mobile devices in the US alone. 

In Q1 Google made just over $2 billion from search in the US on Google.com, out of $6.7 in total revenues. Taking the simplest approach and assuming that Google makes the same amount on every query (which it doesn't), 10% of that Q1 US search revenue would be just over $200 million.

In mobile there are fewer ads but higher response rates. The actual revenue is probably less than $200 million.

If these figures are anywhere in the ballpark, however, it's not crazy to suggest that mobile could be a billion-dollar revenue stream for Google within five years.