Brian at Pajama Market talked today about adding Google Search to your blog. We're not talking about searching the internet. We're talking about searching your previous blog posts.
If youare striving to develop professional trust, be seen as and authority, and have your blog be viewed as a reference, then the ability to search your previous posts is important.
While Brian describes how to accomplish this with Google but I have been setting all my client's blog up using the new Technorati Widget. You can see it in action in my left sidebar under Technorati Tools. Simply type in the search term and click Search. You will be taken to a Technorati page that displays all the posts on my blog in which contain the search term.
I also typically enable the "Blogs that link here" feature of the Technorati Widget. If readers come to your blog looking for information, helping them find it - even if it is on a colleague's blog - is doing them a service.
UPDATE: Currently we are using Lijit for this function.