As an end user, i would love to be able to search for all restaurants lying within a 30km radius around my geographical position ( represented by a latitude and a longitude ).

Given the potential complexity of geographical calculations, which among other must take into account the Earth's sphericity, returning the results for the afore-mentioned query is not trivial. Solr itself is currently being extended ( https://issues.apache.org/jira/browse/SOLR-773 ) to natively support this. A great addition to eZ Find would be to take advantage of this future native feature, and make available to the eZ Find integrators ( template developers and PHP developers ) a way to easily use Geographical search.