Cynthia,
You probably know all about reverse DNS by now, but just in case, take a look at
this FAQ. I wouldn't have thought it was a big deal not to have a reverse DNS entry, as it appears many servers are missing that entry. But as Mike found, it may make a difference with some ISP's, at least in the case of mail servers. In any case you can have St. Louis Internet make sure your web sites are set up properly.
Holly