When it rains it pours. While driving down the information highway, I ran into quite a few articles on the use of chat reference that I would mention.

The first article I found was mentioned on medinfo blog, "Is the collaborative service always superior to the single library service? A project for evaluating the chat reference services in the USA." (in English and free) It is a preprint article in Bibliothek Forschung und Praxis.
Brief blurb:
Chat reference services provided by four types (single academic, single public, consortia academic, and consortia public) of libraries were observed and evaluated. The advantages and disadvantages of both collaborative and single library chat reference service are discussed.


The other three articles I discovered are from Internet Reference Sevices Quarterly. (subscription required)

Using Canned Messages in Virtual Reference Communication by Joseph Straw, 2006 v. 11 (1) 39-49.
Abstract:
More and more libraries are providing virtual reference services for their users. Virtual technologies like e-mail, chat, and instant messaging allow reference librarians to create canned messages to potentially use in different reference situations. The ease and speed in which canned messages can be created is providing ready-made answers to a greater number of reference questions. This article will examine the opportunities and pitfalls of using canned messages in the virtual reference environment, and propose some principles for when to use canned messages in the context of the reference interview.

Instant Messaging and Chat Reference by David Ward, 2006 v. 11 (1) 103-6.
Abstract:
Instant Messaging (IM) is seeing renewed interest among libraries trying to reach out to users and increase their chat reference volume. Younger patrons especially are using IM software as a routine part of their online lives. This article suggests methods and directions libraries can pursue to incorporate IM into their current chat reference services.

Combining the Best of In-Person and Virtual Reference Service to Meet In-Library Patron Needs by Amy VanScoy, 2006 v. 11 (2) 15-25.
Abstract:
When patron workstations are located far from the reference desk, service suffers because patrons can't easily contact staff. While in-house chat services offer a partial solution to this problem, these services fail to provide the face-to-face element that the literature shows is critical for effective reference service. This study analyzes NCSU Libraries' method for solving this problem, a hybrid service that combines features of in-person and virtual reference service.

All of these articles look at the different aspects and issues librarians might encounter when providing virtual reference services such as chat ref. I particularily how NCSU libraries investigated the face to face element. That is an area that we all too often "forget" about when we are looking virtual library services.