I went to it last year. I got six interviews and three waitlists. I didn't pick up any of the waitlist interviews, but a good portion of people picked up at least one of their waitlists. I also did not get a job from the program, but a few people I met there got jobs out of it. But, these people probably would have gotten offers somewhere anyway, because they were at the top of their class.
I would say that it's impossible to know whether it is a worthwhile program for any individual person. Think of it as an OCI, specifically for IP people. I'm sure you've heard stories of people having 10+ interviews at OCI and getting zero call-backs. This could happen to you. On the other hand, you might be the person who gets one interview, and ends up getting a job out of it.
I think the odds are fairly high, if you're a rising 2L with a decent technical background, that you'll get at least one interview. But, there's a cost-benefit analysis that you have to do, and the "benefit" part is pretty hard to quantify.
The way it works is that there are several hundred, or even close to 1000 rising 2Ls and 3Ls walking around this hotel, from room-to-room. The interviews are 20 minutes, like most OCIs, except a lot of the firms are there for 2 entire days. That means that they're probably interviewing 20-30 or more people. Most of these firms will give call-backs to one or 2, or maybe zero people from this fair. So, even if you have a really good resume, and interview really well, the odds are pretty low that you'll get a call-back. You have to remember that most of these firms do regular OCIs and also may take interest in applicants who applied directly to the firm. So, let's say you've got a 1/20 chance of getting a callback on any given interview. Maybe you have six interviews. So, maybe that means you've got a 3/10 chance of getting a callback if you go to the program. Meanwhile, you've got to spend close to $1000 just to go, depending on how far away you live, and the cost of plane tickets. So, is it worth it? If that 3/10 chance of getting a callback turns into a job, then yes. But in this economy, what are the actual odds of getting a callback or of a callback turning into a job? Impossible to know, but probably pretty bad, and probably even worse than the numbers I just threw out there. On the other hand, in this economy, can you really afford to not pursue every potential avenue of employment?
Personally, I will only go back this year if I get 7 interviews. Of course, as a rising 3L, there are far fewer firms willing to even look at my resume.