Here's something I found @ EFFECTIVE COLLABORATION FOR GROUP PROJECTS: THE VALUE OF SYNCHRONICITY by Mercer and Davie. Presented @ TCC 2002.
Online computer conferences or discussion forums (asynchronous CMC) provide a learning environment that supports group collaboration very well. The dialogue of the course is always available so that learners can revisit their discussion, and reflect thoughtfully on their responses. They can then compose and edit messages as their time permits (Burge, 1994; Daugherty & Funke, 1998). However, the feelings of isolation, lack of immediate responses, difficulty making group decisions, and a sense of information overload leave many students quite frustrated (Benbunan-Fich & Hiltz, 1999; Hara & Kling, 1999; Wegerif, 1998). In response students, researchers and online teachers have recommended the inclusion of synchronous communication to asynchronous CMC courses (Bullen, 1998; Carr-Chellman, Dyer, & Breman, 2000; Higgins, 1992; Mason, 1998; Mitchell & Bacic, 2000).
I know that on-line group work without collaboration won't work. In fact in a reflective term paper I wrote a little over a month ago, I suggested that a lack of synchronous communication amongst the members of our project team really hurt us during one assignment.
Indeed many of the "frustrations" listed above were expressed by members of our group. From where I type, the "difficult making group decisions" rises to extreme without synchronous (i.e. chat or "real time") communication.
I'd also suggest that the true value of synchronous CMC (computer-mediated communication)-based education will become fully apparent as we move beyond ASCI or text-based interfaces. Drawings and objects and "virtual" environments to facilitate a community-driven dynamic knowledge base.