I installed PortableApps on my friend's hard drive. It works well!
My friend had no applications on his XP machine, so I installed Portable OpenOffice, Gimp, and several others in a folder I named "PortableApps" in his Program Files directory on drive C. I put shortcuts to the applications on his Quick Start toolbar.
Everything works fine, but Stellarium had to be installed in its own folder on drive C because it can't handle spaces in directory names.
I also like the current PA category structure (e.g. Internet/Browsers/ for Chrome etc.) but I have a suggestion for all those non-official PortableApps that a lot of us is carrying along as well.