The (MS)books say : stored procedures, because of bandwith and server resources usage (see the article mentioned by Mike Cole).

I believe that using sp's for a simple INSERT (or basic SQL) is much overhead for little gain. For more complex queries or actions it might be a good idea to use sp's.

But the most important is : often bandwith and server resources are spoiled using other "bad" habbits, that the gain of using sp's is nothing compared to the loss by those bad habbits ...