Support for widely used Spring Security has been enhanced in upcoming release of IntelliJ IDEA 12 Leda. I would like to highlight some of these changes here.
Spring Security 3.1 Namespace
Full support for all new elements (e.g. <jee>, <session-management>, etc), including completion, navigation and Rename refactoring. Support for all existing tags has also been improved.
Inspections
Many new checks that prevent common setup errors.
Language Injection
Pre-configured support for AOP and SQL (via IntelliLang plugin).
OAuth 1.0 & 2.0
Support for OAuth namespaces (currently for M6) has been added.
JSP Taglib
Even better completion and smart UserDetails (here LDAP configuration) support.
You can try new features already now in IntelliJ IDEA 12 EAP.
Please feel free to give us feedback in comments here or submit bug reports in our issue tracker.

The validations have made our development harder.
Numerous errors are shown even though Spring security has no problems dealing with our configuration.
Notably, messages such as :
‘Multiple elements without ‘pattern’ not allowed’
‘ with pattern ‘/**’ must be last’
Even though we are using the spring-security request-matcher mechanism and often do not include the pattern attibute on the http node for this error to show up.
I don’t remember having the same issues in IntelliJ 10. There has always been issues with referencing beans created via code, namespace handler or otherwise, but this is understandable.