I knew it! I knew there was a PortableApps.com-themed Google start page, but couldn't find it anywhere on the site, so I just gave up - until I installed the PAM 1.2 RC3 and it offered to set it as my homepage.
I had news.google.com as my homepage for the longest time, but that can be cluttered, and it's nice to have Firefox open on something neat and simple.
PortableApps.com is one of the first sites I look at.
Start.portableapps.com is a nice, clean page and it links to both Portableapps.com and news.google.com.
I suppose if I really wanted to be clever, I'd figure out how to make my own Firefox/Google start page and put all of my daily bookmarks around it, throw in a weather widget, something like that, store it on the flash drive (locally saved .html file isn't going to be blocked by work filters). But either I'm not that clever or my ambition isn't there; I don't know, but the Portableapps.com start page is nice.
So it just seems to me, FWIW, that the Start page could be linked from a couple places on the site, e.g. the Firefox Portable page (e.g. "Here's a great site to set as your portable homepage").