I've been going for a few years now, I started because I was a user of their products, I'm not sure whether it was Impromptu or ReportNet at the time. I keep going both to keep in touch and know what's coming down the line.
I wouldn't recommend it for someone who never used Cognos products and who never plans to, but if you're a user, or customer, you might be interested. It's free, so the only cost is your time and transportation. I'm suprised that we don't see many students at this event.
you can access the day's agenda here: http://www.cognos.com/performance2007/na_agenda.html#on_ott
I went to Best Practices in Framework Manager, Keys to Successful Migrations from Cognos Series 7 to Cognos 8 BI and Complete Reporting and Analysis Coverage with Cognos 8 BI.
Those choices might seem strange to you, but remember that I've been using Cognos products for a few years now. If I had to choose again, I would've taken the IBM presentation over the migration session. I
Overall, I don't regret going.