Currently your last 5 searches are saved (if you are logged in). This feature is already in place and makes it easy for you to find that one specific Microsoft Knowledge Base articles again.
At this point, we only save searches that bring back results. We've thought about adding something called "E-mail Searches" (or something, let us know if you think of a better name) that will e-mail you your search results, when a new item is found.
For example, Say you have an error message or code, where that are no articles for. An e-mail search, would let you know when and if an article ever came up that matched that search, or more articles where added that matched your search criteria.
This quite a bit of work, as well as a lot of processor time, so we're waiting for feedback to see if people are really interested in using a feature like this.
Let us know what you think. Use the Feedback link on the left.