Ok, I am a relative newbie to PortableApps do forgive me if these have been covered but here are a few things I'd love to see in PAM:
I initially was going to suggest integrating Launchy (http://www.launchy.net/) but the more I think about it the more I realize it would be much more useful to integrate Launchy-like capabilities into PAM itself, so here is the wishlist:
1 - Configurable hot-key. Win-P is nice but it is not exactly a quick-press. Alt-space, or win-space or some other one-hand combi would work much nicer - so let the user configure it.
2 - Command prompt built into the PAM. When PAM is activated - focus inside a typeable window where you can type commands. When typing into this window - do a quick search of apps, docs, etc. and filter the list so that you can quickly find the app or doc you want. You can use the space where app list is to produce options.
3 - Extension architecture to the #2 - so that other apps can hook into it. So if you type in certain commands, specific actions are to be done (ex "w google.com" would open firefox portable to google.com) Offer an extension that starts indexing the host machine in a temporary space when it starts - so you can have an option of searching through it and launch things not on portable media (a la Launchy)
There is a lot more that can be done in this vein, but I think just the first 2 will make PAM much more usable in the long term