What is stored in mysqld-slow.log?
Queries that exceed the number of second set by long_query_time land in the slow query log.
If you want to parse and examine the mysqld-slow.log file, please use mysqldumpslow.
If you want better ways to examine slow queries, you may want to apply one of the following suggestions:
SUGGESTION #1
Keep in mind that mysqld-slow.log contains slow queries that have finished. It will not record long running queries that are in progress. If you would like to catch queries in the act of running long before they are recorded in the slow query log, please look over my past posts on how to set that up in Query Profiles

Jul 26, 2012 : What is running right now?
Dec 28, 2011 : Is there a tool like Microsoft&#39;s &quot;SQL Server Profiler&quot; for MySQL?

SUGGESTION #2
If you are using MySQL 5.1+, did you know that you could record the slow log into a MyISAM table? That way, you can query the MyISAM table rather than parsing a large text file.
I have past posts on how to set that up:

Mar 30, 2012 : MySQL slow log configuration
Nov 18, 2011 : Create a custom log table in MySQL