Back in the old (pre-BC) days, classes had one role in a raid - classes which were theoretically multi-role were usually forced into a single role, and exceptions were rare. These days, all classes (aside from a few pure dps classes) can have multiple roles, depending on an individual's spec and gear. As such, listing only an individual's class on the calendar signup is almost useless - the people running the raids have to know and remember the roles everyone can fill.

While this can be mitigated a bit by the use of notes, it's silly not to have that information readily available. The primary differentiator for signups should be role - tank, healer, dps (possibly split into ranged and melee), and the class distinctions should be secondary (although still present). In most cases it will be obvious what off-role ability a character will have, based on class (a druid signed up as a tank can do melee dps, and perhaps off-heal; a priest signed up as dps can off-heal; and so on).

Having role based signups will make it much easier for the organizers, who will have a good idea what their needs are in terms of those roles. Having the class information alongside will let them class balance if needed, as well as fill in gaps when a primary role choice isn't available.

You'll be happy to know that this feature is already available. Just need to head on over to the Admin panel, create your Raid Roles with the aptly named "Raid Roles" link, and then select "Signup Type: Role" when you create an event.

The way we did it was to have 4 primary roles: Tank, Healer, Melee DPS, Ranged DPS. Then several secondary roles: Off-healer, Off-tank, Spell Interrupt, CC - Humanoid, CC - Fear, etc.

I currently use role based signups as well. It fits the multi-purpose class structures in place since TBC launch IMO. My only problem with the implementation is this...

Once the calendar event hits it's "Start" time, the display automatically changes to a class based view rather than staying a role-based view and it makes things difficult while trying to assemble the raid. Once the event time is reached I can only view the signup list by:
1. Sort by Class
2. Sort by Time
3. No-Shows

But there is no option to view the list in it's most usable form to me as a Guild Leader trying to get his raid together...by role.

Is there any way that a role based view, post start time, can be implemented on calendar events?

Thanks for the quick reply! That does indeed appear to be exactly what I wanted. Of course, it was only recently that I got access to the Admin controls, so I have a good excuse for not noticing it, at least.