Got a recent e-mail that made me think ... asking me why I almost always use a link to an external source and comment on that instead of writing original pieces. It has certainly been my way in the half dozen blogs I have written over the years. The Web is an unprecedented means of linking together human knowledge and commentary.
So since what you do is always based on the work of others, your teachers at very least, why not? Standing on the shoulders of many giants. I know some who minimize linking so as to keep people at their site. The point here is not to market my knowledge, but to demonstrate how it fits in with my other thoughts and the work of others.