In the 1990's, 10MB was considered a standard mailbox size. This let you send 10-20 emails per day and save email for months. Today 100-150 new emails per day is common--a 10MB mailbox fills in a day at this rate.
The total use of email-like communication is probably still increasing. However, pure email--as measured both in number of emails per day and average size of email--appears to have plateaued. The main cause is the growth in alternative email-like methods of communication that offer similar reliability and ease of use. Examples include cell phone text messaging (SMS) using full keypads, email embedded in enterprise applications (e.g. SalesForce.com) and new social networking portals with embedded email-like communication (e.g. LinkedIn and Facebook).
Bob Spurzem - In addition to his role as Ferris analyst, Bob is director of product marketing at Iron Mountain Digital Division, which was recently purchased by Autonomy.