There are a few places where search can fail in a distributed environment, but when configuration is not quite right, there are no indications of errors or logging.
Increased logging of failures would help troubleshoot such problems, as well as lower the "I get 0 results, why?" questions that come across the mailing lists.
Areas where logging would be helpful:
search app cannot locate search-servers.txt
search app cannot find searcher node listed in search-server.txt
search app cannot connect to port on searcher specified in search-server.txt
searcher (bin/nutch server...) cannot find index
searcher cannot find segments
Access denied in any of the above scenarios.
There are probably more that would be helpful, but I am not yet familiar to know all the points of possible failure between the webpage and a search node.