Paul Ballard on common Web Service mistakes.
I try to avoid posting link-only entries since I try to not feel totally useless in my own blog, but this is a really good article that has good points for consideration when building a Web Services architecture for your project. Building web-services in .NET is so damn easy that it's tempting to simply put in a [WebMethod] and forget all about it - it works, it's accessible and it gets the job done. The article gives a few easy optimization tips and caveats. Good read.