Yes, we have "search within topics" on our todo list, but it would require an entire rewrite of our search system, which is just something we don't have the resources for right now.
With that said, I don't know of any time I've not found something that I know exists with either the built in search feature or the Google search feature. Searching is definitely an art, but I honestly believe it is pretty easy to find stuff if you learn how to search. Using all the options in search, including wildcards and boolean search operators can make a huge difference.
One of the more powerful features of the search is how to use wildcards. These wildcards make search VERY powerful on a forum, especially one with as many posts as we have here.
"Using an asterisk at the end of your search term will find many variations of the term you seek.
Example: If you enter the Search: child* you'll be returned with information on children, child, childs, etc.
You can also use other "Boolean search operators like AND, OR, NOT.
Learning how to use the asterix and the AND OR NOT and you'll be able to find pretty much anything you are looking for.
Oh, here are some geek links if you really want to be a search master:
Cool video: http://www.youtube.com/watch?v=vube-ZcJFk4
Really geeky: http://en.wikipedia.org/wiki/Boolean_logic