I'll be publishing an extensive review of the Foleo after the product is officially announced (we're technically in a pre-announcement phase at the moment). By the time the Foleo is released, mDayscape, a third party Palm Desktop equivalent, will be available. Without an onboard PIM to sync to the Treo, it's currently not the ideal GTD platform, unless you keep your system in Word or text files.
Without direct access to a Foleo, critics are trying to draw broad conclusions about the device based solely on its specs, which, due to its form factor, compare unfavorably to a laptop's. It's really a PDA in a subnotebook form factor, so there's no boot time, no shutdown time, no disk caching (it's solid state, sans hard drive), no need to manually save files in progress.
The instant-on feature really is as great as Palm claims it is. There have been 10-minute windows of time that I would never dream of using with a laptop (half the time would be lost to bootup and shutdown intervals), but are great for the Foleo, where it's possible to process several emails or look up something online. The battery life is robust enough for an overnight charge to power the unit all day (6 hours of cumulative use got the unit down to 15% by the end of the night). You can leave the charger at home, just as you would your cell phone.
Since the Foleo is Linux based and is quite different than most consumer laptops except in its form factor, adoption of the Foleo will depend on how platform-agnostic your general purpose computing really is. If 80% of what you do on a laptop is email, web browsing and document editing (Docs To Go is its native suite for Office-compatible files), there's a good chance you're in the target market for this device. If you need something more platform-specific, like Quickbooks, Revit or Illustrator, you'll probably need to carry a laptop throughout the day anyway, so the Foleo would be extra baggage. Palm is mainly touting it as an email solution, and though I was initially puzzled by the emphasis, processing email on the Foleo really is more efficient and satisfying than a handheld or a laptop. It's definitely worth testing one out for yourself when its released in the next few weeks.