OK, since I think I fuelled the flames of this discussion somewhat, let me add my 2 cents:
As a beginner, its really hard to look at someone and tell whether their doing good technique, unless you have someone doing REALLY bad technique nearby. However, felling good technique vs. bad technique as uke is very easy.
Next, the reason its nice to have hakama, or some other symbol of rank is to aid in choosing partners in class. When we are doing techniques that I've fairly familiar with, I'll choose the nearest person as my partner, regardless of rank- I can usually help people who know even less than me get the general idea of the technique, and I will usually learn a lot from someone who's my sempei. But when sensei has us do a technique thats extremely complicated, difficult, or very new to me, I try to find someone with a hakama or a brown belt, or who I know is more experienced than me so that I don't spend the entire time we have to work on the technique trying to figure out the first half of it. I'm not sure how I'd act at a seminar, but I think I'd be happy to work with pretty much anyone- its much harder to judge the ability of someone you've never seen before, and you certainly can't base you judgement simply off of their clothes, especially with every school having slightly different rules(Hell, I don't even know if my school has a cohesive policy on hakama)
I'm not sure if hakama's build excessive egos, but I don't think that its that much of a valid argument against them- first of all, in aikido the level of arrogance(sp?) is amazingly low. Second, ANY symbol of rank is likely to inflate people's egos, whether it is a polka dotted belt and green pajamas or a hakama.
In any case, I think that at a seminar, when surrounded by lots of people you don't know, you should be doubly attentive and polite- its much easier to step on people's toes when in unfamiliar settings.