Haven't kept up on the web-based (aka: free amateur) fanfics, but type in "Baker Street Irregulars" and you'll find references to plenty of professional authors using the Sherlockian universe (that is, those fanfic/pastiche-writers who actually get paid to do it!). You'll see names like August Derleth (his "Solar Pons" series of books), Vincent Starrett, and bunches of others. (Hell, even Basil Rathbone wrote at least one little ficlet (http://www.basilrathbone.net/potpourri/daydream.htm) that we know of!)