Most sites with search either already offer autocomplete search as you type into the search box, or are planning to implement it soon. And most search vendors now offer at least a passing support for this feature.
There can be technical issues with latency and how the page gets rendered in the browser, but search engines are addressing these too, and technical aren't likely to be totally blocked on this.
However, one area that should be thought about more is where these search suggestions will come from. There are many ideas in the industry, and sites may decide to do a combination of things.
Example sources for Autosuggest / Autocomplete suggestions:
- Dictionary based – this is labor intensive and is best used only for specific occasional overrides
- Specific URL suggestion based
- Word index based – the search engine taps its own index of document phrases – implementations vary by vendor
- Search Logs – the main issue here is to filter out any potentially objectionable language
- Taxonomy matches – suggest specific nodes in the taxonomy
- Page Title matches – suggest the titles of specific pages
- A hybrid combination of these
Other technical / design items:
- How to match – just the beginning or more advanced matching
- What happens when the user clicks or selects a suggestion – do you show search results, or go directly to a page.
- Check that suggestion being offered will actually bring back results