I've had clients who rave about LookSmart. One B2B client says she gets more qualified leads from LS than from Google & Overture combined.
At $.15 a click, I think it's worth the investment if you have a well-written description containing your major keyword phrases. You can be #4 on MSN's SERPs paying much less per click than the first 3 Overture results.
Keep in mind that the 10 keywords you get to associate with your LookSmart listing when you sign up, don't apply to MSN's results, so it's very important to put your main terms in your description.
Lot's of people have a knee-jerk hate response when it comes to Looksmart. Mention LS to some webmasters and you can see their jaws clench. Looksmart has a definite "image problem" with the decision makers in the internet industry. This disgust with LS almost seems like a default reaction, reminiscent of the way people hate their utility company or a weasily politician. Many people would love to see Looksmart dry up and blow away.
However, "image problems" aside, if you read the above thread you will see there exist real advantages to using Looksmart and in many cases you could be missing some opportunities by not listing with LookSmart.