[quote name='jh6269']Depending on what AmEx card you have, that might have been the problem. I remember seeing a show about credit cards once where they said that the American Express cards that do not have limits actually hurt your ability to get credit. It was sort of confusing, and this was years ago, so I don't know if it's true anymore.[/QUOTE]
It'll look like 100% utilization if you aren't careful. Instead of reporting your credit limit (you don't have one), your highest reported balance will be reported. If you're consistent in your charging patterns, your highest reported balance will be pretty close to your current reported balance every month, and you look like you're using the whole limit of the card or even going over it.
The trick to beating this is to have one month where you charge up a pretty big number, then keep subsequent months of charges significantly lower than this. But of course, don't spend money you wouldn't normally spend just to do this, and always pay in full each month.