NEW YORK (AP) -- New federal regulations designed to speed up the processing of checks went into effect on Thursday, and consumer advocates advised Americans to be more vigilant about monitoring their accounts. The Check Clearing for the 21st Century Act -- better known as Check 21 -- will allow financial institutions to exchange electronic images of consumers' checks rather than transporting the actual paper checks around by air, land and sea. As a result, checks that consumers write are likely to clear faster than before, so there will be less "float" between the time a check is written and...