On the Ready
Given the fact that we are only now (and I mean in the last six months or less) emerging from the New Millennium Depression, it's surprising how many people I see using employment development centers and dressed as though they're going to the park or kicking around on a Saturday afternoon to do housework.
The people who are at these centers are active job seekers. They are there to spend time actively looking for open positions for which they may apply and interview. But it doesn't seem that they're making the connection that one of those positions may respond while the job seeker is still sitting at the computer by saying, "I just looked at your resume and I'd like to interview you at 2 p.m. today (2 p.m. being about an hour later). Can you be here?"
When conducting a job search, it's important to dress as though you'll be interviewed at the drop of a hat. The person you pass on the bus or ride with on the elevator may be the one who will be interviewing you 30 minutes later. In the alternative, they may be the one who gives you the lead of a lifetime -- it lands you your dream career.
Appearance is one of the factors that speaks volumes about what you think of yourself, your attention to details, your personal expectations for standards of conduct and quality. So to go to any career center in casuals indicates either you're not serious about the job search or you're not a serious worker. It's important to go to a career development center ready to be sent on a job referral that day. It's important to be ready to be interviewed.
Now this doesn't mean you go dressed in your dry clean only worsted suit. No. That's too expensive and too dressy. But the attire you would expect to wear in the real office situation is appropriate for going to the career development center, class, shopping, just about anywhere and everywhere. The critical issue here is preparedness.
You never can tell when an opportunity will arise. Yes, it may be a scheduled interview several days from now. It may also be a spontaneous opportunity. It may be that after interviewing at the temporary placement office, the recruiter is impressed enough that they want to send you to work right then and there.
So the question is really one that needs to be asked before leaving the front door every day.
"Am I ready for the interview?"

Yvonne,
Great points. Let me elaborate a bit on your point about being properly dressed. I'm often asked by candidates how they should dress for an interview. The answer is that they should be dressed the same way that they will dress for work should they be hired for the position. If they don't know, I tell them to call the organization and ask.
Organizations that require jackets and ties (are they any left?) will not look kindly upon a candidate showing up in business smart clothes (i.e., khaki pants and button down shirt) and definitely not casual (i.e., jeans and a polo shirt). If people in your position at the organization are wearing suits to work, then you should wear a suit to your interview. If they're wearing casual clothes, then you should as well. But beware, it is dangerous to dress even slightly more casual than those with whom you will interview. So if there's any doubt at all, dress slightly less casual than those with whom you will interview. If they're typically in jeans and polo shirts, then a great strategy is for you to dress in khaki pants and a button down shirt.