=) Well to each their own. The Get Satisfaction Live Labs profile was, in fact, the official Photosynth forum for the first seven months, so if the Photosynth team trusts them, then so do I.
It's also worth pointing out that there's no particular reason why you have to join GetSat with your WLID... there's no particular bonus or connection with your Photosynth account if you do... just a convenience to you, if you prefer that option, and the sign-in form (if you do choose the WLID option) is made by the Windows Live ID folks themselves, so I just don't have an issue with it.
The .NET Passport (which was later renamed to Window Live ID) was originally designed by Microsoft to be your one login across the web (just as Facebook Connect is actually succeeding at more than anyone before them) so it isn't as though GetSat is doing something with your WLID that isn't intended by the WLID team.
...Regardless, you're just not comfortable with it. To each their own.