Last week I ran a poll on twitter about the new features of syslog/ng 3.10 and the wildcard-file() source was voted the most.
Starting with version 3.10, syslog-ng can collect messages from multiple text files. You do not have to specify file names one by one, just use a wildcard to select which files to read. This is especially useful when you do not know the file names by the time syslog-ng is started. This is often the case with web servers with multiple virtual hosts. From this blog you can learn how to get started using the wildcard-file() source.