Personally, my favorite project using Spring Security was one combining Spring Security and Wicket. I love Wicket, it's an incredibly fun framework to develop UIs in, and the integration with Spring Security (2) at the time was very elegant and easy.
I would not recommend Spring Security if you already have a complex, homegrown system that suits the needs of the business. In this case, it can be difficult to justify the effort and learning curve of replacing something homegrown with something out of the box and functionally equivalent - although as a technologist, I would love to, it can be hard to make a good argument to business sponsors.
Hope that answers your question!
Author, Spring Security 3 (the Book), Packt Publishing, 2010
Joined: Dec 16, 2003
Thanks that answers my questions!
I agree, convincing the business sponsors is tough at times