RSS Feed by category & search items

Hi,
I wanted to provide a way for my users to subscribe to RSS Feeds matching particular search items only. However the usual <b>?s=</b> doesn’t work. In fact it just returns the front page with results matching the search.
Similarly I want to provide a way for my users to subscribe to RSS Feeds matching a particular category only. Again the usual idea doesn’t seem to work.
Is it something already available? My search didn’t yeild any results.
Please let me know if that is so.
Otherwise please consider them as feature requests.
Is there any timeline already decided for these features?
Thanks,
Angsuman