I feel adding the ability to search on the user name of the Author of post would be great for two reasons:
1) We could find our own (older) post easier. Sometimes one forgets the thread titles one has posted in...and they roll off the recent post list...and you would like to go back and see what else was written, but can't find the old thread in a search result.
2) Some posters here have many great post. Their post are very much worth reading. It would be great to be able to see what other gems the particularly talented members of webmasterworld have posted earlier. On other boards, one can search on post contributed by a given username -- and see the results as either threads or post (with text excerpts).
The ability to obtain a search results page giving all post by a given user name would be beneficial to the community over time.
It would also help to be able to specify a range of time for post returned by search; i.e. last X days or a specific Month and/or year.
Adding a time range to search would make the number of results more manageable when the user name has lots of post; it would also reduce bandwidth by making the number of post returned smaller than the complete set of all post made by users having hundreds of post.