I tested a preview version of Microsoft Lync, the chat-and-communications component of Microsoft Office 365 (since then, the final version has been released). Lync has a competitive feature set, but the stability of the service and the way the features were implemented when I tested it left a lot to be desired.
The first step with using Lync for group videoconferencing is to set up an account with Office 365, which is a bit of administrative overhead all by itself. Users and conference leaders alike both need to have accounts, which follow the format firstname.lastname@example.org. The Lync client's login interface has a misleading "e-mail address" as well as "user ID" entry field; both needed to be filled out with the same onmicrosoft.com address.
If you'd rather host Lync on your own hardware, instead of via Microsoft's Office 365 service, a standalone server version of Lync's back end is also available.
Lync clients exist for both Windows PCs and Macs (as well as iOS, Android and Windows Phone devices), but the Windows and OS X clients are totally dissimilar. The former uses the Windows 8 "Modern UI" visual style, but the latter doesn't even look like a native Mac app, which made it difficult to figure out how things worked. Whiteboarding didn't seem to work at all on the Mac client, for instance, despite repeated attempts. Navigating the UI on the Windows side was also tricky, because the behavior of many of the controls wasn't always clear.
Most of the in-conference functions are similar to what's available in the other applications I tested: text chat (either to individuals or the group); automatic focus following, so that whoever's speaking takes prominence in the video feed; local recording of a chat; interactive desktop or application sharing; quick group polls; and the ability to provide a document to the whole group as an attachment.
PowerPoint slide decks and OneNote documents can also be presented to the group interactively, without needing either of those programs running.
The biggest stumbling block was the program's overall performance. Even on high-end systems with plenty of bandwidth, audio and video both stuttered far more often than the other apps tested here, a sign that the back end's performance was more to blame than the client.
Microsoft's integrated messaging and conferencing solution still feels unfinished. Laggy video, an inconsistent Mac client and a complicated back end setup process don't help.