A charge authorization is different from an actual charge. The charge is what will post, the authorization is just a check on the card (e.g., when you hold the ticket).

Merchants are very lax in releasing authorizations -- hotels, car rentals, etc. all put larger authorizations on your card than they need, and when they figure out how much to actually charge you (when you check out, return the car, etc.), they seldom release the excess authorization, and it falls off the card after several days. Not a big deal if you have a huge credit line, but it could be if you don't, or are close to maxing it (or if you use a debit card with a low balance, though if you use a debit card you deserve whatever happens to you, IMO ).

There's some fighting here in CA between the state and gas stations, who typically put authorizations on for about $70 for a fill-up, though the average tank is about half that these days, and they don't release the auth when you're done. So we may start seeing a little more accountability for authorizations in the future...