Hi Henning,
For the WWW version of Hoogle this means that data must be transmitted constantly and I think that rises a privacy problem. I don't want that my typing behaviour can be observed and analysed somewhere. Such technique would also require JavaScript which is disabled in browsers of security oriented people.
The current version of Hoogle already uses Javascript to do a few things (setting focus, adding quick search) - but if javascript is disabled it still works perfectly well. I will stick to this design principle. I haven't thought too much about the front end, as the front end is comparatively easy compared to the back end stuff. Once I have thought about it, I'll release something for feedback, and will be happy to incorporate anyones suggestions. AJAX'y and auto-complete would save me time when using Hoogle, so I would like to add it, but of course will take privacy very seriously. Thanks Neil