Chris Anderson provides a good introductory course on the economics of the Information Age, but doesn't tell us what we don't already know.
Code and algorithm to hashtag a string in ASP.NET Web Forms. Written in VB.NET, includes working demo.
Expanding on my earlier post about auto-hashtagging text: Now, we can put the hashtagged text into a MySQL table.
Use PHP to extract terms from a MySQL database table and automatically tag an input string with those terms.