In the security code I switched from gnu.regexp to jregex library. The reason is performance improvements. Indeed, gnu.regexp is the slowest library in java.
The fastest in the package java.util.regexp but, so far we are 1.3 compatibles so I picked jregex which is pretty good. Not as good as java.util.regexp but very close. To give you an idea, gnu.regexp is about 30 times slower than the java.util.regexp package.
To give you an idea, when benching a forum page, gnu.regexp was taking 40% of the total time. The forums abuse security, they make lot of security calls.