How to set up OpenSearch in Drupal? I would like to set up OpenSearch so it works in Drupal 7 so the search experience can be integrated with the user browser the way it is done on drupal.stackexchange.com.

I found the following contrib modules (none ported for D7):


http://drupal.org/project/opensearchplugin - D5, D6
http://drupal.org/project/opensearch - D6
http://drupal.org/project/opensearch_aggregator - D5, D6


What is the current solution for this for D7 ?
From looking at these three modules closer, I see that only the opensearch module has a 7.x branch: https://drupal.org/node/74142/release.  You could try using that branch, but it probably not ready for a production system.  

It looks like Kiam is the module author you may be able to contact him to find out if he is planning to complete the Drupal 7 version.