There are lots of challenges! Here are but a few:
1) "listening" for an association is made more complicated by the acronym thing. For instance, I have alerts set up for "ASHA": I have come to learn that there are LOTS of people named Asha out there, as well as several other associations with the same acronym: American Saddlebrook Horse Assn, American Sports Hockey Association and, my favorite, American Social Health Association (focus is on STDs!). Then someone in England named Asha was murdered, so lots of results about that lately. I have refined my searches as much as I can, but I still have to weed through a LOT of unrelated stuff.
2) Sharing internally: Basically doing this kind of listening makes you a de facto member of the customer service dept. Which means that you need to know who does what on staff so you can direct questions to the appropriate people. If you have a small staff it's easier, but we have a staff of 250. I've been here over a year and a half and am STILL trying to learn who is responsible for what. What's been helpful for me is working with customer service (called action center here) to go through the training they go through and also our intranet which has an expertise search feature.
3) Logging information into the AMS. I haven't really done this yet but know I should be. But the question is what kinds of interactions do you log? If someone complains about dues or something else about the association on Twitter, do I log that in the database? Comments on Facebook? Positive comments? The fact that they retweeted something?
4) Timely responses. What do you do when you see something on Facebook on a Saturday afternoon and need to either alert another staff member or ask around to get an answer? How do you deal with the gap between the M-F 8:30-5 mentality vs. the real-time nature of the social web?
5) Comfort level of the masses with Facebook and Twitter. There are many people out there who are still not comfortable with using Facebook and/or Twitter for business--including association staffers. There are people on staff who, when I ask them the answer to a question that's been posed on our Facebook page, answer "Tell the person to email me--that information doesn't belong on Facebook." "That information" being a something on our public website, of course. Ditto Twitter, our forums, etc. People are not universally comfortable with the one-to-many form of response; they still want to email an individual person, which does nothing for the other eyes on the question posed on a public social network.