Something to bear in mind is that regex is actually a declarative programming language like prolog : your regex is a set of rules which the regex interpreter tries to match against a string.   During this matching, the interpreter will assume certain things, and continue assuming them until it comes up against a failure to match, which then causes it to backtrack.  Regex assumes "greedy matching" unless explicitly told not to, which can cause a lot of backtracking.  A general rule of thumb is that the more backtracking, the slower the matching process.

It is therefore vital, if you are trying to optimise your program to run quickly (and if you can't do without regex), to optimise your regexes to match quickly.

I recommend the use of a tool such as "The Regex Coach" to debug your regex strings.

http://weitz.de/files/regex-coach.exe (Windows installer) http://weitz.de/files/regex-coach.tgz (Linux tar archive)