I have listened to a wide range of them, and I cannot recommend these. I expected to get information about capabilities of the various companies' products, but instead I got something more akin to the pitch one would give trying to get funding to develop the project, for example, the size of the market and the major pain points (for example, I cannot count the number of times that presenters belabored the point that computer viruses and SPAM were costing companies massive sums). Additionally, the overheads (registering, sitting through the intros and polling) routinely exceed the miniscule useful content -
In many of these presentations, you can download the slides and quickly page through them to see if the speaker will say anything useful. Also note that my experience was that many of the presenters had not practiced their presentations before giving it to the audience (which the polls showed were often several hundred people). All in all, they often demonstrate real contempt for the audience's (potential customers') time.
However, this being said, there were a few companies that did very good presentations. Electric Cloud (makefiles) is a real standout.