Using 454 to do microbial ecology / metagenomics of environmental / soil samples?
Then I think you should take a look at this paper.
Quince, C., Lanzén, A., Curtis, T., Davenport, R., Hall, N., Head, I., Read, L., & Sloan, W. (2009). Accurate determination of microbial diversity from 454 pyrosequencing data Nature Methods, 6 (9), 639-641 DOI: 10.1038/nmeth.1361
The Pathogens blog has a good summary post on it.