I found this video introduction on Guice very good. Guice is another Inversion of Control (IoC) container, much like Spring IoC, but with the advantage of coming later. What's particularly interesting about Guice is that it largely forms the basis of JSR-299's IoC.
I'm a big user of Spring IoC and frankly don't have a problem with it. However I can see that Guice could save me some wiring code and, therefore, potentially bugs (not that there are bugs in my code!). I might well consider using Guice for future projects. The outcome of JSR-299 will weigh in heavily on this decision though as I like my code to be as standards-compliant as possible.
One thing that I am comfortable about with Spring though (vs Guice) is that my beans have no knowledge of being injectable; they simply are by being bean conforming. With Guice you must declare what is potentially injectable. I do like the loose coupling between my bean code and the IoC that Spring provides, yet I can see that Guice, by declaring what is injectable, can save some of the wiring code.
I'll guess I'll just have to give Guice a whirl to find out.