> You can opt for the breathalyzer in most states, or they'll take you back to the office for a blood test.

Please correct me if I'm wrong, but I was under the impression that if you opt out of a breathalyzer, they'll still charge you with a DUI and the courts will consider the breathalyzer refusal as an equivalent to being intoxicated.

Almost. Yes, you may still be charged. Yes, they may use the evidence of your refusal. As far as equivalence, no: the test itself is just one piece of evidence. Because refusal should ordinarily make it more difficult to prosecute DUI (for what is, comparable to the stop, a very small inconvenience), I think most states have an automatic license revocation penalty attached to it - usually around six months. Field sobriety tests (e.g. walk in a straight line), I think, are much less conclusive and do not have such requirement.

IANAL. Search for James Duane.

Most (all?) states have the law written that if you refuse a breathalyzer it is an automatic license suspension. Depending on other evidence the state may press DUI charges.