This is my experience how the user expectation and Autocompleter 126.96.36.199 differ on WP 3.3:
1. Type "mi" into the field
2. You're shown matching results, but they're sorted alphabetically. A more desired solution would be to show them in an order of likely importance (posts starting with "mi" shown first, then posts with words starting with "mi", then the rest shown in the order of how early in the post title "mi" is) - now "Abcd Efgh Ijkl Family" is shown before "Mileage Matters"
3. Click one of the results
4. Whether the autosubmit on select is set on or off, the form doesn't autosubmit on click.
5. The clicking deselects the form, so to get back there, you have to click it again if there's no search button or you like pressing enter.
6. Submit the form by pressing enter if you didn't click the search button.
7. The user is, indeed, directed to a search page. Not the post page. Unless you have a separate plugin that redirects search to a single post page when the search returns only a single post. Autocompleter 188.8.131.52 doesn't step in between to do it.
At the moment Autocompleter improves the user experience in a very slight way, but the abovementioned quirks may leave users frustrated which is bad for the user experience. We don't consider it deployable until a newer version remedies these shortcomings.