With XP-friendly drivers finally cropping up, making the trip much less troublesome, it's time to "downgrade" any Vaio Ps still stuck with Vista. Though U.S. WWAN drivers still have to be prized from Vista packages -- ignore the ones at that link, they're for European Ps -- that's the only laborious part left. GPS and most of the fancy keyboard controls work just fine.
Kudos goes to Jenn of Pocketables, chief among those who figured out everything there is to figure out in this particular niche of netbookdom.
XP runs so much better on the P than Vista it feels like an entirely different machine. It's markedly faster than Windows 7, too, making it worthwhile even if you're got that installed. Even the XP versions of Sony's system management utilities are markedly less bloated.
How did this sorry need to tinker come about? The Vaio P has 2GB of RAM, meaning Microsoft won't license Windows XP for it. Sony itself seems to have realized the mistake it made putting Vista on a netbook: it's reportedly planning to release a 1GB model with XP.