As noted by John Munsch, MyJavaPack looks pretty cool. At first glance, it looks like an open-source version of Open Logic's Blue Glue. Since I actually did some work on Blue Glue this summer, I downloaded MyJavaPack and did a a quick install.
I was quite impressed. All it did was download the packages I requested and installed them. In most cases, this is what I want - especially on my machine where I already have everything setup. Blue Glue goes a bit further than MyJavaPack. It installs and configures everything for you. This is great for brand new machines, but can be a pain for pre-configured machines since it adds stuff to your PATH.
The thing I like about MyJavaPack is that it's open-source. Therefore, I might be able to dig in and customize it for an AppFuse-based installer. Such an intaller would include tools for developing AppFuse: Ant, Tomcat, MySQL, Eclipse and AppFuse. That'd be pretty cool to be able to download and install an entire development environment.
Neither product does what we all really want: the ability to do an "update" (like Windows Update or Software Update on OS X) of our existing packages.