Working with Accountemps means that you'll likely be able to find something pretty quickly, but mostly for only the short term (a few weeks or months). The problem comes when a good company wants to keep you, but they are stuck as hiring you permanently would cost them substantially more than if they took their time to find another employee without an agency representing them. When economy is tougher, it is highly unlikely you'll end up serving the company for longer than a few months and then end up training a replacement they find for half the amount they pay the agency.
The benefit though is that you can rely on pretty steady pay, just keep in mind that it shouldn't be a long term plan if you ever want benefits such as vacation time (paid out on each paycheck), medical plan, or rrsp matching.
Reliable Short Term Employment Solution
Little Chance for Permanent Placement