We're experiencing some problems with the Photosynth site just now.  Early indications are that we're having a hardware issue, but we're digging into that as we speak.  We're working to resolve it as fast as we can.  In the meantime, we're moving to our backup servers now, so we expect to be back shortly...

Update 2:50 PM:  We're back.  Turns out our main database machine developed a disk problem.  We failed-over to our backup database machine, and now we're back up and running.  Apologies for any inconvenience this may have caused you.....

Update 3:25 PM: We didn't lose any data during our outage, but if you were trying to create a synth right around that time and it seems to be taking an inordinately long time to complete, you might try it again, giving it a different name.