It can be sparse to get traffic, but if you are willing to go beyond 5 cent bids (that seems to be where everyone is at the moment, so not really viable unless you put together massive keyword lists and even then there is not enough traffic in a ot of cases). I have found by focusing on specific words and writing specific ads my click-throughs have shot up astronomically with them.
I can take the same keyword, same bid price and run it on a broader ad but very related and get almost no clicks. Pull it out into its own order write a very specific ad and clicks increased 5000%. Like I said, the broader ad was not off-topic and was relevant, just not as specific.
Some traffic sources seem more friendly to broader ad matching, and MSN does not seem to be one of them, at least not for me.