When you go to a conference or some other event where everybody wears a nametag, pay closer attention to the nametag design. There are many subtle usability mistakes that I see far too often.
First of all, is your name easy to read? It's called a nametag, after all; the name and affiliation of the wearer should be the most prominent thing on the tag. I've been to events where the most prominent thing on the nametag was the name of the conference itself. Hey, everybody presumably already knows what conference they're attending. It's printed on the agenda sheet, it's printed on the tote bag, it's printed on every sign at the venue, it's even printed on the pens you gave out, for goodness' sake. Tell them something they don't know: Who they are talking to. (Corollary: Don't put the name at the bottom of the tag.)
Okay, now that you've got the name on the nametag in a position and style where it actually serves its purpose, you have to make sure the tag is visible when worn. Most computer events use a lanyard-style nametag. If the lanyard length is not adjustable, then you have a new problem: You have to make the cord long enough to go around the wearer's head. But once you do that, the cord is now so long that the nametag itself hangs around the wearer's belly-button. This is already awkward enough, but if the conference entails sit-down meetings, the nametag will end up into the wearer's lap. And if you have the meetings at tables, the nametag will disappear beneath the surface of table. A nametag that you can't see isn't doing its job.
Great, you have a name on the nametag that people can see, you are keeping the tag visible, you think you're home free. But wait, how is your nametag mounted to the lanyard? Nearly all lanyard nametags I've seen are mounted from a single clip or hole at the top center. With this design, the nametag can easily flip around, pushing the person's name into their chest and showing the nametag's backside to the rest of the world. One solution to this problem is to make the nametag reversible, so that even if it flips, the name is still visible. Another solution is to mount the nametag from two holes, one in each top corner. In this manner, the nametag becomes flip-resistant.
Just a few little details in nametag design. But you'd be surprised how many people miss them. (The PDC nametags are the only one in recent memory that addressed all three problems.)