While the additional suggestions many have put for would be really nice, all I want for the time being is the ability to label my guildmates with notes so that I can remember who the hell I'm talking to!
Sure, it's very easy to identify Hordo and myself, due to our fairly static naming conventions, but others don't do this, and it can be difficult to remember that Sorglyphia and Adenosi are the same person, especially when you start tacking on 3, 4 of 10 names to that list of alts.
And using the Friends List as a fix for this is poor, since the list has a finite number of slots, which could
easily be filled just by friending all of my guildies, and I'd then have no room for friending folks who I group with outside of guild.