Managing Coder Estimates

I just submitted a little job to RentACoder (converting an ASP.NET site to PHP for easier hosting - I'm not much of a PHP developer) and part of their new wizard has a bit about estimates. You can supply a deadline, or you can ask the bidders to estimate how long the job will take, based on your specifications.

But there's a warning:

Even the best coders do not estimate accurately. If you don't understand and account for this, it will probably cause you unnecessary problems.

Do you understand that it's wisest to multiply any coder estimate by either 5 or 2 to get a more realistic estimate?

I like that. Multiply by either 5 or 2. Pick one. That's about as accurate a method as any.