if you go to a good LS, they'll be so many recruiting events it will be unavoidable.
I'm already worrying about these things ... wtf do you do/ say at them?
nothing to worry about. i did a bunch of research on the firm the first time i went to one... and it was TOTALLY unnecessary. most of the lawyers just want the free food and drink, too.
but seriously, i did try to find out a bit about each firm before i got too wasted. i asked about hours (since you really can't do that during oci), what types of cases they were working on, how soon they were able to do stuff like taking depositions (as opposed to doc review), why they choose that firm over others, did they work on pro bono projects (and could they bill that time), and about the structure of the firm--how work's assigned, and whether you move around in different departments as a summer associate there.
most people didn't do any of this.... the lawyers were mostly penn grads, so a lot of them would just reminisce about law school. some people avoided the lawyers altogether and just drank.
basically, you'll get what you want to out of the experience, but no way is there anything to be nervous about.
as to matthies: yes, if you go to a lower-ranked school, or have sucky grades, then you'll want to join the ABA and your local bar association. i'm a member of mine, and i have spoken to a lot of practicing attorneys by going to events. i probably won't be practicing in philly, tho, so it really doesn't matter as far as getting a job. like the vast majority of my classmates, i will be getting my job though oci.