Just got 2 marriage certificates back, very quickly. Interesting to note that there is no parental information so it doesn't say Joe Smith, son of William - for example.
What was really helpful for me was that the clerk filling out my gggrandmother's name misspelled it (which was the spelling used in the online database) but when she signed it, she spelled her name correctly and included her middle initial which was very helpful to my research. Also I was able to track down some of the witnesses/officiants to Ouachita Parish - though their handwriting was hard to read.
One more note, in case it helps anyone, they put an official stamp on the back of the document and the sent one of the certs with the stamp bleeding through the middle of the main part of the document. I was able to send it back and get a better copy and it was no big deal.