It would be fun to play around with the laser distance mechanism to see if you could design a speed gun with this thing. I would hope they would allow developers access to the appropriate APIs to allow this. It wouldn't be good for police work, but it would be fun the average consumer. The price needs to come down quite a bit, though.

It's huge and heavy: 260mm x110mm x 70mm weighing more than a kilogram. Not something you would put in a pocket, and only to be "handheld" for a short time.

Nope, it's usually multi-layered and dim and wet and dampness poses one of the biggest problems for gear, generally. The thickness of the cover not only makes solar-power really impossible, but makes getting a GIS signal generally impossible, too. If someone makes it possible, a lot of us would be ecstatic. NASA [nasa.gov] gives a hand [osd.mil] and remote sensing helps, but under a canopy as dense as rainforest can be is about as remote as you can get these days, where satellite at least makes it possible to establish contact with something in the middle of deserts and oceans.

GPS, Differential GPS, and WAAS isn't accurate enough for high quality survey work. All of these of limited accuracy of more 1 meter, whereas any decent survey should measure error hopefully less than 10 millimeters.

Wrong, each of these technologies is sufficiently accurate for surveying. GPS alone has (can have) an error rate of less than 2cm over 50 miles. You just have to have a known point. Everything can be calculated in real time or post processed. Most systems like this (certified for surveying) are well into the $20ks, unfortunately.

Good Resouce: http://www.icivilengineer.com/Surveying/GPS/

P.S. It can take up to 5 minutes to get a single point, even in the clear. If your under even a moderate tree cover, you're screwed with GPS.