Debugging in the (Very) Large describes Microsoft's challenges in implementing Windows Error Reporting. Those challenges include TBs of data, 1 billion+ computers running WER, and multiple entities accessing that data (anyone that can afford a VeriSign certificate can use WER for their own Windows applications and drivers). Worth a look (hey, it is even a SIGOPS paper).

Lucene (in the Java and .NET versions, at least) does not create a parse tree when you use Lucene(.Net)?.QueryParser.QueryParser.Parse() to parse your queries. Instead, Lucene rewrites the query into a set of parenthesized terms that are either optional, required, or prohibited -- i.e. AND, OR, and NOT operators are replaced by +, -, or nothing (optional terms have no prefix).