I've tried 4.2, but didn't see anyway to move the panel to vertical so I could line it up on the right or left screen edge. The option is there, but it will not allow me to move it there, unlike 4.0.
I could just as well edit the .xfce4 files to do the same as I did in 4.0.
But, after compiling the CVS version from their website, I really didn't notice too many differences (worth the upgrade, IMHO). The most noticeable were:
1. More GUI settings for all desktop features, like "resolution", "screensaver", "hinting" and "anti-aliasing", and some others. However, I can do the same currently with config files.
2. Gradient support for screen backdrop. Pretty nice.
3. Better Session Management support.
4. Automatically picks up Gnome/KDE apps and configures in Desktop menu.
5. Icons in Desktop Menu.
* Overall, the CVS version they have out currently is pretty nice, but I went back to 4.0. I think I'll wait til they release it and AL'ers make a package for it.
Oh yeah, in addition...the 4.2 version has a buggy "xffm" in my opinion. You will even get an error compiling it and you have to downgrade to avoid your console filling up with debug messages. The version they recommend currently seems to give me a "signal 11" as well. I guess that's what you can expect from CVS versions.