I have to say, I'm very happy with the results. I'm now sitting at a YSlow (V2) score of 75; 90 if I use the "Small Site or Blog" ruleset. I believe I can improve this by adding expires headers to my images, js and css. More than anything, I'm impressed with wro4j, its great support and easy setup. I was looking for a runtime solution (b/c I didn't want to have to rebuild Roller) and it seems to be perfect for the job. Furthermore, wro4j minifies everything on the fly and they'll have an expires header filter in the next release.
JAWR and the YUI Compressor are other alternatives to this filter, but I'm currently sold on wro4j. First of all, it passed the 10-minute test. Secondly, it didn't require me to modify Roller's build system.
At this point, if I'm going to implement JS/CSS concatenation and minification in AppFuse and Roller, wro4j seems like the best option. If you disagree, I'd love to hear your reasoning.