In the past week, hundreds of Trefis members have created forecasts for two key drivers of Yahoo's ( YHOO) stock value: (1) Search Market Share and (2) Revenue per Search (RPS).Their forecasts suggest that Yahoo!'s search market share will trend slightly higher than the Trefis forecast, and that Yahoo! will gain share from Google ( GOOG) and Microsoft ( MSFT) Bing, AOL ( AOL), and Ask.com. Search advertising is Yahoo!'s most important division, constituting 25% of the $21 Trefis price estimate for Yahoo! stock. Given the importance of the search advertising business, Yahoo!'s stock is quite sensitive to (1) Search Market Share and (2) Revenue per Search (RPS). Below are charts showing recent estimates created by Trefis members for the two drivers.