Jeans/Polo Shirt (usually tucked in)/Sneakers combo that far too many people wear in a professional setting. I'm at a semiconductor engineering conference right now and it's waaaaaay to easy to figure out who are the right people to talk to and who are just engineer dweebs looking for some free stuff.

Would it kill you to put on a button-up shirt and some nicer shoes as you try to represent yourself professionally? A jacket or sport coat doesn't hurt, either.