Isn't this just common sense?
Anyone who still has a landline but doesn't use an unlisted number is in the same boat, really. You're just a http://whitepages.com search away.
Very few people that are making synths have cameras with GPS sensors built in. What's more, these don't work indoors - you need a direct line of sight with the satellites who provide the GPS location.
Ultimately, different people are going to make different choices about personal security, but I can't possibly imagine taking tons of photos of my house and the things that fill it with the plan to upload them to a site like Photosynth without considering whether or not to make the synth private or not or whether to geotag the synth or not.
Geotagging your synth is usually a very manual process which many people don't even know how to do, so again I can't imagine doing it without considering the consequences.
It's fair to warn people; I just don't know how someone wouldn't think this through.